Ajax calls for "files" and "files_trashbin" apps (WIP)

:construction: WIP

Frontend:
- The files app list now uses ajax calls to refresh the list.
- Added support the browser back button (history API).
- Added mask + spinner while loading file list

Backend:
- Added utility function in core JS for parsing query strings.
- Moved file list + breadcrumb template data code to helper
  functions
- Fixed some file paths in trashbin app to be similar to the files app

TODO:
- fix tab/space issues in source files
- error case for non-existent dirs
- breadcrumb resizing after ajax call
- test in other apps (encryption?)
- test in all browsers