I have removed the directory management features from Gitter and ported them to GitList,
since they are application-specific logic. I was unhappy with the way directories and multiple
directories were handled, so i altered almost everything.
The tests are OK, but the coverage is not good. This means that i'll need som help from all
GitList users that are actively testing the development version with multiple directories.
I have removed the directory caching feature for now, it will be re-implemented soon.
Instead, we select a default branch - master by default, but the default
branch can be configured using config.ini.
Note that if the default branch does not exist in a repo, that should
not cause any issues.
Also adds phpunit to composer.json's require-dev section.
