Various bug fixes and improvements

- Bettah comments in code at some places
- Fixed bug where $_POST['bt_quicknote'] would get set on a page where
it was not even available.
- Fix bug where the ID would not get put in the linktree on the edit
page
- Now recounts all the project info when recounting statistics
- Fixed bug where an entry would get marked as opened again when going
from unassigned <-> WIP or vice versa
- Fixed bug where marking multiple entries would increase/decrease the
same amount of open entries from all projects
- Fixed bug where the mark_read row for the entry being marked would get
deleted.
- Changed the project edit template
- Project Manager: Changed "Remove" to "Actions", now also displaying an
Edit button
- Removed duplicate text strings ($txt['progress'], $txt['add_entry'])
- Organised English language file