[ticket/10631] Stagger the enable/disable/purge for extensions

PHPBB3-10631
[ticket/10631] Use display name if available

PHPBB3-10631
[ticket/10631] Validation for extensions

PHPBB3-10631
[ticket/10631] Remove code duplication

PHPBB3-10631
[ticket/10631] Additional validation

PHPBB3-10631
[ticket/10631] Make the enable/disable/purge notices more visable.

PHPBB3-10631
Merge pull request #921 from imkingdavid/ticket/10444

[ticket/10444] Do not default to the previous post edit reason.
[ticket/10631] Remove references to delete extension

PHPBB3-10631
[ticket/10631] Fix some issues as noted in github comments, significantly simplified validation

PHPBB3-10631
[ticket/10631] Use exceptions for errors. Build action list dynamically.

PHPBB3-10631
[ticket/10631] Simplify exceptions

PHPBB-10631
[ticket/10631] Update tests

PHPBB3-10631
[ticket/10631] get_extension_metadata_manager -> create_extension_metadata_manager

PHPBB3-10631
[ticket/10631] Fixing an error in the test script

PHPBB3-10631
[ticket/10631] A _start_ on a metadata manager test.

No idea if it runs without errors, I do not have the testing stuff setup.

PHPBB3-10631
[ticket/10631] Fix class construct arguments in test

PHPBB3-10631
[ticket/10631] Metadata manager tests

PHPBB3-10631
[ticket/10631] Functional acp_extensions test, cleanup

PHPBB3-10631
[ticket/10631] Fix metadata_manager_test

PHPBB3-10631
[ticket/10631] Various front-end fixes (extensions manager)

Add Back button from details

Add cancel button from actions

Correct language strings

PHPBB3-10631