Complete Finnish translation

Based on main master branch.
Added Henri Koivuneva to AUTHORS.
Merge.
Turkish translation completed.
Added Mehmet Özgür Bayhan to AUTHORS
Merge.
Added mezzatheme themes marketplace to features list.
Use new decorator "richhtext_filters"

The decorator "richtext_filter" is marked as deprecated.
Method to load all symbols of all files in a submodule
Move gallery related tests into the app directory

If the app is not installed, the tests are not executed.
Move blog related tests into the app directory

If the app is not installed, the tests are not executed.
Move page related tests into the app directory

If the app is not installed, the tests are not executed.
Move account related tests into the app directory

If the app is not installed, the tests are not executed.
Move form related tests into the app directory

If the app is not installed, the tests are not executed.
Move core related tests into the app tests directory

These tests do not belong direct to an specific app, so they stay
in the core app directory for now.
Simplify new test module structure.
Provide a common TestCase class for all app specific tests, for features such as admin user plus debug cursor for query tracking. Also consistent naming for tests.
Move tons of tests into their correct apps.
Added Thomas Rega to AUTHORS.
Whitespace cleanup