Bump dependencies on core and composer-plugin.
Reindent composer.json.
Cleanup event registration.
Fix author annotations.
Add factory.
Reformat .travis.yml.
Add sudo: false to .travis.yml.
Apply the git-depth hack to make travis happy again.
Bump Contao Core versions to above 3.2 and add conflict for 3.4.0.
Drop Contao 2.11 code.