[ticket/12160] Add function to check if phpBB is installed.

PHPBB3-12160
[ticket/12160] Check if phpBB is installed before creating phpBB container.

PHPBB3-12160
[ticket/12160] Move phpbb_check_installation_exists() to functions_install.php

PHPBB3-12160
[ticket/12160] Use phpbb_check_installation_exists() in the other modules.

PHPBB3-12160
[ticket/12262] Also find vars array when it's defined in the trigger_event()

PHPBB3-12262
[ticket/12262] Fix location list for acp events with "Locations:"

PHPBB3-12262
[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
[ticket/12262] Do not use getExtension()

The method is php 5.3.6+ only.

PHPBB3-12262
[ticket/12262] Do not use inline assignments

PHPBB3-12262
Merge remote-tracking branch 'maelsoucaze/develop' into develop

* maelsoucaze/develop:
  [ticket/12272] Fix hardcoded colons in subforums.
  [ticket/12272] Fix hardcoded colons in subforums.
Merge pull request #2111 from nickvergessen/ticket/12262

[ticket/12262] Fix event exporter

* nickvergessen/ticket/12262:
  [ticket/12262] Do not use inline assignments
  [ticket/12262] Do not use getExtension()
  [ticket/12262] Fix location list for acp events with "Locations:"
  [ticket/12262] Also find vars array when it's defined in the trigger_event()
[prep-release-3.1.0-b1] Update version to 3.1.0-b1
[prep-release-3.1.0-b1] Add migration for 3.1.0-b1
[prep-release-3.1.0-b1] Prepare Changelog
[prep-release-3.1.0-b1] Add changelog for 3.1.0-b1
[prep-release-3.1.0-b1] Update build version to 3.1.0-b2-dev
Merge branch 'prep-release-3.1.0-b1' into develop

* prep-release-3.1.0-b1:
  [prep-release-3.1.0-b1] Update build version to 3.1.0-b2-dev
  [prep-release-3.1.0-b1] Add changelog for 3.1.0-b1
  [prep-release-3.1.0-b1] Prepare Changelog
  [prep-release-3.1.0-b1] Add migration for 3.1.0-b1
  [prep-release-3.1.0-b1] Update version to 3.1.0-b1
[ticket/11239] Including username before Overview title

Adding username to the page title to avoid confusion while managing
multiple users in ACP

PHPBB3-11239
[ticket/11071] Add fallback if requested style don't exist

PHPBB3-11071