Prometheus - Donation and payment store

Web

1. Fixed miscellaneous PHP error notices and deprecations.
2. Several code improvements across the board.
3. Editing a theme now works again.
4. Theme editor icon now displays correctly.
5. Editing or creating a theme no longer changes the active theme to the theme you are currently editing.
6. Fixed dashboard graph labels (they no longer say "undefined").
7. Made sure files in the install folder cannot be reached directly, this also applies to a lot of other files that are normally protected by htaccess (when using apache) or the nginx config too.
8. The "updates" area no longer throws an internal server error.

Important notice: If you have any custom standalone pages they must now set the ABSPATH constant before including functions.php or any other file that should be access protected.

Modified files

Web

1. Pretty much all files have been touched because of the ABSPATH change