Use on-root resources for 404 and 403 HTML
Blurred glass theme and other CSS

* Redesign Glass theme to synergise with blurred article backgrounds
* Added background pseudo-blurring
* Moved Options, Feedback and Sync to the top bar
Hot Information banner
Make image URL filter case insensitive
Lower thread title below info banner
Toggleable mnemonic visability

Removes the need for logging out to hide mnemonics
Fallback BG for glass and no custom banner
Clear blur, if no custom BG is set in glass theme