[ticket/12271] Decouple dropdown header and footer from #notifications_list

PHPBB3-12271
Merge pull request #2128 from nickvergessen/ticket/12271

[ticket/12271] Decouple dropdown header and footer from #notifications_list
[ticket/12272] Fix hardcoded colons in subforums.

In subforums list, under the parent forum description, there are two
harcoded colons instead of {L_COLON}.

PHPBB3-12272
[ticket/12272] Fix hardcoded colons in subforums.

In subforums list, under the parent forum description, there are two
harcoded colons instead of {L_COLON}.

PHPBB3-12272
Merge remote-tracking branch 'maelsoucaze/develop' into develop

* maelsoucaze/develop:
  [ticket/12272] Fix hardcoded colons in subforums.
  [ticket/12272] Fix hardcoded colons in subforums.