Fixes issue with csp becasue of caching

- Uses html-loader partials (removes ejs)
 - Updates select styling

Giving up on better else/catch/finally formatting -- can't fight anymore
Switching to tabs for better accessibility
https://twitter.com/sh4na/status/1146837957200027648

Lays some groundwork for the coming timeline webview

Splits App into AppBase & AppWithConfigBase for impl of new webviews

Adds the gitlens icon to settings editor and welcome page

Changes changelog image links to permalinks
Moves all images for docs into a docs folder
Removes unused images

Removes Uri monkey patch as it no longer will work
See 03432806c8
Stops encoding uris in .toString calls

Adds menu & toolbar settings to the settings editor
Adds mode setting for settings editor
Adds sticky header to settings editor