[ticket/11098] Add mark/unmark all options to remember me keys

PHPBB3-11098
[ticket/11098] HTML Validity fix to Notifications in UCP

PHPBB3-11098
[ticket/11098] Update subsilver2 to also include mark/unmark all buttons

PHPBB3-11098
[ticket/11098] Fix error reporting on the autologin key pages

PHPBB3-11098
Merge remote-tracking branch 'vsephpbb/ticket/11098' into develop-ascraeus

* vsephpbb/ticket/11098:
  [ticket/11098] Fix error reporting on the autologin key pages
  [ticket/11098] Update subsilver2 to also include mark/unmark all buttons
  [ticket/11098] HTML Validity fix to Notifications in UCP
  [ticket/11098] Add mark/unmark all options to remember me keys