[ticket/12483] Allow to setup extensions before database and functional tests

PHPBB3-12483
[ticket/12483] Add a .sh that moves an extension in place

PHPBB3-12483
[ticket/12483] Move schema files into tmp/ and only copy them when needed

PHPBB3-12483
[ticket/12483] Require the extension manager class

PHPBB3-12483
[ticket/12483] Close database connection when tearDown() is called

Similar to phpbb_database_test_case::tearDown()

PHPBB3-12483
[ticket/12483] Use file_put_contents()

PHPBB3-12483
[ticket/12483] Fix copyright in prepare_extension.sh

PHPBB3-12483
[ticket/12483] Fix finder usage when generating the schema.json file

PHPBB3-12483
[ticket/12483] Remove unused globals

PHPBB3-12483
[ticket/12483] Fix selectors for installing extensions in functional tests

PHPBB3-12483
Merge remote-tracking branch 'nickvergessen/ticket/12483' into develop-ascraeus

* nickvergessen/ticket/12483:
  [ticket/12483] Fix selectors for installing extensions in functional tests
  [ticket/12483] Remove unused globals
  [ticket/12483] Fix finder usage when generating the schema.json file
  [ticket/12483] Fix copyright in prepare_extension.sh
  [ticket/12483] Use file_put_contents()
  [ticket/12483] Close database connection when tearDown() is called
  [ticket/12483] Require the extension manager class
  [ticket/12483] Move schema files into tmp/ and only copy them when needed
  [ticket/12483] Add a .sh that moves an extension in place
  [ticket/12483] Allow to setup extensions before database and functional tests