Merge pull request #2309 from Nicofuma/ticket/11366

[ticket/11366] Extension's version's check

* Nicofuma/ticket/11366: (29 commits)
  [ticket/11366] Fix headings css in list page
  [ticket/11366] Add config value in schema_data.sql
  [ticket/11366] Fix HTML
  [ticket/11366] Exchange links and settings' form
  [ticket/11366] Remove the extra {S_FORM_TOKEN}
  [ticket/11366] Move the links to the top of the page
  [ticket/11366] Hide the version check settings by default
  [ticket/11366] Versions, options and actions heading should be centered
  [ticket/11366] Better language string for "recheck all"
  [ticket/11366] Move "recheck all" link
  [ticket/11366] Add $config['extension_force_unstable']
  [ticket/11366] Use force_cache on the list page
  [ticket/11366] Add recheck-all link
  [ticket/11366] Force the use of the cache on the list page
  [ticket/11366] Update FILE_NOT_FOUND language string
  [ticket/11366] Fix whitespaces
  [ticket/11366] Update FILE_NOT_FOUND language string
  [ticket/11366] Update var names
  [ticket/11366] Align language strings
  [ticket/11366] Fix detailed view
  ...
[ticket/11467] Add language variables for extension exception messages

Remove hard-coded messages and add language variables for extension
exception messages.

PHPBB3-11467
[ticket/11467] Add language variables to tests

Convert the hardcoded strings to language variables.

PHPBB3-11467
[ticket/11467] Add user object to extension manager for tests

PHPBB3-11467
Merge pull request #2432 from Nicofuma/ticket/11226

[ticket/11226] filespec::move_file() should error correctly

* Nicofuma/ticket/11226:
  [ticket/11226] Explicity set file_moved to false
  [ticket/11226] Add tests
  [ticket/11226] Use $user->lang()
  [ticket/11226] filespec::move_file() should error correctly
Merge pull request #2511 from Marshalrusty/ticket/12611

[ticket/12611] Remove phpBB Group copyright notice from .gifs

* Marshalrusty/ticket/12611:
  [ticket/12611] Remove phpBB Group copyright notice from .gifs
[ticket/11942] Don't change the reason to '' when hard deleting

PHPBB3-11942
[ticket/10073] Add a contact administrators page and refactor email forms.

The message to be displayed on top of the email form cannot be configured yet.

PHPBB3-10073
[ticket/10073] Replace board_contact mail with links to contact page

Error pages still contain the email address.

PHPBB3-10073
[ticket/10073] Add Admin contact email template

PHPBB3-10073
[ticket/10073] Use namespaces and fix all class names

PHPBB3-10073
[ticket/10073] Fix code sniffer complain

PHPBB3-10073
[ticket/10073] Global announcements have a forum_id now

PHPBB3-10073
[ticket/10073] Fix grammar in comment

PHPBB3-10073
[ticket/10073] Add doc blocks to new classes

PHPBB3-10073
[ticket/10073] Remove unneccessary todos he config switch is enough

PHPBB3-10073
[ticket/10073] Add @config_text to admin_form

PHPBB3-10073
[ticket/10073] Use get_username_string and correctly sprintf for languages

PHPBB3-10073
[ticket/10073] Fix title for "Email topic"

PHPBB3-10073
[ticket/10073] Fix missing language string

PHPBB3-10073