replace js image scaling with css for message attatchments

See merge request !3

Can now collapse server categories.
Client remembers collapse state, incl. advanced appearance settings.

Remove Hardcore Mode.

- replaced many uses of `as any` with another more specific cast `as T`
- filled in missing typed for items that needed to be typed
  - new runtime code was added where necessary to satisfy the new types with comments
- added missing theme variable "sidebar-active" to the Theme variables
- forms using `react-hook-form` are now typechecked
- changed some instances of `target` into `currentTarget` while removing `as any` assertions

Re-design blocked messages.

Fix keyboard focus on mobile.

Fix settings theme colour.

Update colours in main app.