Updated the admin interface

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.

src/main.rs

@@ -1,6 +1,6 @@
 #![forbid(unsafe_code)]
 #![cfg_attr(feature = "unstable", feature(ip))]
-#![recursion_limit = "256"]
+#![recursion_limit = "512"]
 
 extern crate openssl;
 #[macro_use]