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

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

PHPBB3-11979
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