Add GitLab saver, apply common lingo to Git savers (#3931)

* Transform GitHub saver to work with GitLab as well

You can choose which provider you want to use, the data is given in the
same place.

I tried to avoid code duplication, so service providers' unique
properties are in separate files, the settings of the selected provider
are loaded.

In two fields I am not sure that it fits into the current structure:

* module-type: gitservice
  Which module is a `gitservice` type, it will be listed in the
  drop-down menu.
* default-api-url: https://gitlab.com/api/v4
  The default URL to access the provider's API.

This is just a sketch, not a final version, suggestions for modification
are welcome!

* Rename saver from GitHub to GitService, update docs

* Split GitHub and GitLab to separate savers, apply common lingo

Sadly, it doesn't seem to make much sense to search for common parts in
the code, because there might be a Git service that is very different
from the GitHub API (such as BitBucket). Therefore, I feel that Git
savers are not able to share other than the translations.

I deleted the defaults values from the translations and set it to the
text entry because they should not depend on the translations.

* Add more information about the password field

It is not clear how to create a personal access token, thus added a link
to the help pages. In addition, GitLab only accepts personal access
token, GitHub also accepts the password, so I made this clear.

* Extract commit message to lingo

* Fix indentation

* Use improved base64 encoder

Fix conflict with a06acc4eb8

core/modules/savers/gitlab.js

@@ -0,0 +1,120 @@
+/*\
+title: $:/core/modules/savers/gitlab.js
+type: application/javascript
+module-type: saver
+
+Saves wiki by pushing a commit to the GitLab REST API
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: true */
+"use strict";
+
+/*
+Select the appropriate saver module and set it up
+*/
+var GitLabSaver = function(wiki) {
+	this.wiki = wiki;
+};
+
+GitLabSaver.prototype.save = function(text,method,callback) {
+	/* See https://docs.gitlab.com/ee/api/repository_files.html */
+	var self = this,
+		username = this.wiki.getTiddlerText("$:/GitLab/Username"),
+		password = $tw.utils.getPassword("gitlab"),
+		repo = this.wiki.getTiddlerText("$:/GitLab/Repo"),
+		path = this.wiki.getTiddlerText("$:/GitLab/Path"),
+		filename = this.wiki.getTiddlerText("$:/GitLab/Filename"),
+		branch = this.wiki.getTiddlerText("$:/GitLab/Branch") || "master",
+		endpoint = this.wiki.getTiddlerText("$:/GitLab/ServerURL") || "https://gitlab.com/api/v4",
+		headers = {
+			"Content-Type": "application/json;charset=UTF-8",
+			"Private-Token": password
+		};
+	// Bail if we don't have everything we need
+	if(!username || !password || !repo || !path || !filename) {
+		return false;
+	}
+	// Make sure the path start and ends with a slash
+	if(path.substring(0,1) !== "/") {
+		path = "/" + path;
+	}
+	if(path.substring(path.length - 1) !== "/") {
+		path = path + "/";
+	}
+	// Compose the base URI
+	var uri = endpoint + "/projects/" + encodeURIComponent(repo) + "/repository/";
+	// Perform a get request to get the details (inc shas) of files in the same path as our file
+	$tw.utils.httpRequest({
+		url: uri + "tree/" + encodeURIComponent(path.replace(/^\/+|\/$/g, '')),
+		type: "GET",
+		headers: headers,
+		data: {
+			ref: branch
+		},
+		callback: function(err,getResponseDataJson,xhr) {
+			var getResponseData,sha = "";
+			if(err && xhr.status !== 404) {
+				return callback(err);
+			}
+			var requestType = "POST";
+			if(xhr.status !== 404) {
+				getResponseData = JSON.parse(getResponseDataJson);
+				$tw.utils.each(getResponseData,function(details) {
+					if(details.name === filename) {
+						requestType = "PUT";
+						sha = details.sha;
+					}
+				});
+			}
+			var data = {
+				commit_message: $tw.language.getRawString("ControlPanel/Saving/GitService/CommitMessage"),
+				content: $tw.utils.base64Encode(text),
+				branch: branch,
+				sha: sha
+			};
+			// Perform a request to save the file
+			$tw.utils.httpRequest({
+				url: uri + "files/" + encodeURIComponent(path.replace(/^\/+/, '') + filename),
+				type: requestType,
+				headers: headers,
+				data: JSON.stringify(data),
+				callback: function(err,putResponseDataJson,xhr) {
+					if(err) {
+						return callback(err);
+					}
+					var putResponseData = JSON.parse(putResponseDataJson);
+					callback(null);
+				}
+			});
+		}
+	});
+	return true;
+};
+
+/*
+Information about this saver
+*/
+GitLabSaver.prototype.info = {
+	name: "gitlab",
+	priority: 2000,
+	capabilities: ["save", "autosave"]
+};
+
+/*
+Static method that returns true if this saver is capable of working
+*/
+exports.canSave = function(wiki) {
+	return true;
+};
+
+/*
+Create an instance of this saver
+*/
+exports.create = function(wiki) {
+	return new GitLabSaver(wiki);
+};
+
+})();