[ticket/11979] Add ability to create dropdown menu to prosilver

PHPBB3-11979
[ticket/11979] Fix errors in dropdown

PHPBB3-11979
[ticket/11859] Make avatar drivers return template filename

The service name might not follow the expected naming scheme which would
cause abnormally long filenames and confusion for authors that might add
more avatar drivers.

PHPBB3-11859
[ticket/11859] Add missing get_template_name method to test drivers

PHPBB3-11859
[ticket/12064] Delete obsolete viewsource.html file from adm/style/

PHPBB3-12064
Merge remote-tracking branch 'cyberalien/ticket/11979' into develop

* cyberalien/ticket/11979:
  [ticket/11979] Fix errors in dropdown
  [ticket/11979] Add ability to create dropdown menu to prosilver
[ticket/11241] Add dropdown control button.

PHPBB3-11241
[ticket/11241] Consolidate topic actions into "Topic tools" dropdown.

PHPBB3-11241
[ticket/11241] Use DEFINE for the block.

PHPBB3-11241
[ticket/11241] Fix the dropdown in RTL languages.

PHPBB3-11241
[ticket/11241] Add events & var for extensions to dropdown.

PHPBB3-11241
[ticket/11241] Add border to dropdown menu options.

PHPBB3-11241
[ticket/11241] Fix the disappearing dropdown when responsive changes take effect

PHPBB3-11241
[ticket/11241] Retain button gradient when menu is active.

PHPBB3-11241
Merge remote-tracking branch 'prototech/ticket/11241' into develop

* prototech/ticket/11241:
  [ticket/11241] Retain button gradient when menu is active.
  [ticket/11241] Fix the disappearing dropdown when responsive changes take effect
  [ticket/11241] Add border to dropdown menu options.
  [ticket/11241] Add events & var for extensions to dropdown.
  [ticket/11241] Fix the dropdown in RTL languages.
  [ticket/11241] Use DEFINE for the block.
  [ticket/11241] Consolidate topic actions into "Topic tools" dropdown.
  [ticket/11241] Add dropdown control button.
[ticket/12061] Fix keyboard shortcut in firefox

PHPBB3-12061
[ticket/12067] Remove double scrollbar from notifications dropdown.

PHPBB3-12067
[ticket/12069] Add core.submit_post_end event

PHPBB3-12069
Merge pull request #1925 from imkingdavid/ticket/12069

[ticket/12069] Add core.submit_post_end event
[ticket/12069] Fix event documentation

PHPBB3-12069