[ticket/11491] Move file to correct directory

PHPBB3-11491
[ticket/11491] Fix class name of functional test

PHPBB3-11491
[ticket/11491] Add extension_acp_test.php to functional group

PHPBB3-11491
[ticket/11491] Fix path to the ext/ folder

PHPBB3-11491
[ticket/11491] Correctly remove the store/temp_ext/ directory after use

PHPBB3-11491
[ticket/11491] Only copy files from phpBB/ext/ the directory exists

PHPBB3-11491
[ticket/11491] Copy files back only if we saved them previously

PHPBB3-11491
Merge remote-tracking branch 'nickvergessen/ticket/11491' into develop

* nickvergessen/ticket/11491:
  [ticket/11491] Copy files back only if we saved them previously
  [ticket/11491] Only copy files from phpBB/ext/ the directory exists
  [ticket/11491] Correctly remove the store/temp_ext/ directory after use
  [ticket/11491] Fix path to the ext/ folder
  [ticket/11491] Add extension_acp_test.php to functional group
  [ticket/11491] Fix class name of functional test
  [ticket/11491] Move file to correct directory