[ticket/11531] Add basic set of functional tests for new avatar system

This currently includes tests for the gravatar, remote avatar, and upload
avatar drivers. The local avatar driver is currently not supported. Two
tests currently fail and have been marked as incomplete. One failure is
due to an issue with Symfony's DomCrawler that exists in Symfony < 2.2.
The other one is caused by a bug in the way remote avatars are treated.
According to my tests, this bug also exists in phpBB 3.0.11 and has been
reported in the tracker: http://tracker.phpbb.com/browse/PHPBB3-11534

PHPBB3-11531
[ticket/11531] Add acp and ucp groups functional tests for avatars

The test for the acp and ucp groups settings are currently marked as
incomplete due to a bug that causes the settings to not show an error
when incorrect data is entered. However, the avatar data is not saved.
That means that even though the error treatment seems to correctly work,
the user is never informed of the issues with the submitted avatar data.

PHPBB3-11531
[ticket/11531] Use assertContainsLang() where possible

PHBB3-11531
[ticket/11531] Remove incomplete flags for tests after merging PR #1404

Issues should be fixed by the now resolved ticket PHPBB3-11535:
http://tracker.phpbb.com/browse/PHPBB3-11535

PHPBB3-11531
Merge branch 'develop' of https://github.com/phpbb/phpbb3 into ticket/11531
Merge branch 'develop' of https://github.com/phpbb/phpbb3 into ticket/11531
[ticket/11531] Add changes for supporting modified testing framework

Additionally, the groups avatar is deleted after the avatar tests in the
ucp groups page in order to prevent issues with other tests that expect
that no avatar has been set for the admin group.

PHPBB3-11531
Merge branch 'develop' of https://github.com/phpbb/phpbb3 into ticket/11531
[ticket/11531] Use abstract class for avatar tests and unify test cases

PHPBB3-11531
[ticket/11531] Reduced amount of avatar functional tests to minimum

The tests were reduced to only test one case that should be correct and one
that should fail. Different test cases have been split up over the specific
test files for the acp groups, acp users, ucp groups, and ucp users page.

PHPBB3-11531
[ticket/11531] Check if uploaded avatar is properly displayed in tests

PHPBB3-11531
Merge pull request #1401 from marc1706/ticket/11531

[ticket/11531] Add basic set of functional tests for new avatar system