doc: fix some minor issues (links, order, shortcut)

- [x] Add shortcut (`Ctrl+,`) for Setting dialog on the doc
- [x] Add `Editor Watcher Timeout` and `Editor Options`
- [x] Rearange level of titles and order of links

docs/WebUI/import-export.md

@@ -3,7 +3,7 @@
 Similar to [draw.io](https://app.diagrams.net) it is possible to load and continue editing PlantUML diagram images.
 
 
-# Export a diagram
+## Export a diagram
 
 Via the editor menu or <kbd>Ctrl</kbd> + <kbd>S</kbd> (or <kbd>Meta</kbd> + <kbd>S</kbd> in the case of a Mac) you can open the file save dialog.
 Here you can edit the file name, choose a file/diagram type and download the diagram.
@@ -12,7 +12,7 @@ The default is to download the PlantUML code.
 ![export](https://raw.githubusercontent.com/plantuml/plantuml-server/master/docs/WebUI/gifs/diagram-export.gif)
 
 
-# Import a diagram
+## Import a diagram
 
 This feature is based on the PlantUML meta data which currently **support only PNG and SVG** diagrams.
 Besides a diagram image, you can of course also load a diagram code file.