Add hooks mechanism and th-opening-default-tiddlers-list hook

see: https://github.com/Jermolene/TiddlyWiki5/issues/1064

boot/boot.js

@@ -1899,6 +1899,36 @@ $tw.boot.isStartupTaskEligible = function(taskModule) {
 	return true;
 };
 
+/*
+Global Hooks mechanism which allows plugins to modify default functionality
+*/
+$tw.hooks = $tw.hooks || { names: {}};
+ 
+/*
+Add hooks to the  hashmap 
+*/
+$tw.hooks.addHook = function(hookName,definition) {
+	if($tw.utils.hop($tw.hooks.names,hookName)) {
+		alert($tw.hooks.names[hookName]);
+		$tw.hooks.names[hookName].push(definition);
+	}
+	else {
+		$tw.hooks.names[hookName] = [definition];
+	}
+};
+ 
+/*
+Invoke the hook by key 
+*/
+$tw.hooks.invokeHook = function(hookName, value) {
+	if($tw.utils.hop($tw.hooks.names,hookName)) {
+		for (var i = 0; i < $tw.hooks.names[hookName].length; i++) {
+			value = $tw.hooks.names[hookName][i](value);
+		}
+	}
+	return value;
+};
+
 /////////////////////////// Main boot function to decrypt tiddlers and then startup
 
 $tw.boot.boot = function() {

core/modules/startup/story.js

@@ -58,6 +58,8 @@ exports.startup = function() {
 			window.location.hash = "";
 			var storyFilter = $tw.wiki.getTiddlerText(DEFAULT_TIDDLERS_TITLE),
 				storyList = $tw.wiki.filterTiddlers(storyFilter);
+			//invoke any hooks that might change the default story list
+			storyList = $tw.hooks.invokeHook("th-opening-default-tiddlers-list",storyList);
 			$tw.wiki.addTiddler({title: DEFAULT_STORY_TITLE, text: "", list: storyList},$tw.wiki.getModificationFields());
 			if(storyList[0]) {
 				$tw.wiki.addToHistory(storyList[0]);				
@@ -116,6 +118,8 @@ function openStartupTiddlers(options) {
 	}
 	// Process the story filter to get the story list
 	var storyList = $tw.wiki.filterTiddlers(storyFilter);
+	//invoke any hooks that might change the default story list
+	storyList = $tw.hooks.invokeHook("th-opening-default-tiddlers-list",storyList);
 	// If the target tiddler isn't included then splice it in at the top
 	if(target && storyList.indexOf(target) === -1) {
 		storyList.unshift(target);