Add first view tests (repository creation)

Merged username-removed-26331 requested to merge grote/repomaker:view-tests into master
  • splits up view tests and model tests into different modules
  • adds CI checks to ensure tests do not write outside test_dir
  • adds tests for login in single and multi-user mode
  • adds first tests for repository views

After this MR is merged, all newly styled views should come with tests.