Drag and drop images in the editor to import and insert (#5699)

* Merge

* Clean up

* More clean up

* Ensure image import works when type is not set, clean up post import actions

* Removed spurious new line

* For non image files insert a tiddler link

* Added documentation for new settings and features

themes/tiddlywiki/vanilla/base.tid

@@ -1550,6 +1550,58 @@ html body.tc-body.tc-single-tiddler-window {
 	width: 10%;
 }
 
+
+/*
+** Tiddler editor dropzone
+*/
+
+.tc-dropzone-editor {
+	position:relative;
+}
+
+.tc-dropzone-editor.tc-dragover .tc-editor-toolbar::after{
+	z-index: 10000;
+	top:0;
+	left:0;
+	right:0;
+	height: 100%;
+	background: <<colour dropzone-background>>;
+	content: "<<lingo DropMessage>>";
+	pointer-events: none;
+	position: absolute;
+	display: flex;
+	align-items: center;
+	justify-content: center;
+	background-color: <<color background>>;
+	border: 4px dashed <<color modal-border>>;
+	font-weight: 600;
+	font-size: 150%;
+	opacity: 0.8;
+	color: <<color foreground>>;
+}
+
+.tc-editor-importpopup {
+	width: 100%;
+	height: 100%;
+}
+
+.tc-editor-import {
+	position: absolute;
+	top: 50%;
+	left: 50%;
+	transform: translate(-50%, -50%);
+	background: <<color pre-background>>;
+	box-shadow: 2px 2px 10px <<colour foreground>>;
+	padding: 10px;
+	width: 96%;
+	border: 1px solid <<color tiddler-controls-foreground>>;
+	text-align:center;
+}
+
+.tc-editor-import img {
+	max-height: 500px;
+}
+
 /*
 ** Storyview Classes
 */