Mostly updated the admin interface, also some small other items.
- Added more diagnostic information to (hopefully) decrease issue
reporting, or at least solve them quicker.
- Added an option to generate a support string which can be used to
copy/paste on the forum or during the creation of an issue. It will
try to hide the sensitive information automatically.
- Changed the `Created At` and `Last Active` info to be in a column and
able to sort them in the users overview.
- Some small layout changes.
- Updated javascript and css files to the latest versions available.
- Decreased the png file sizes using `oxipng`
- Updated target='_blank' links to have rel='noreferrer' to prevent
javascript window.opener modifications.
