Tests + Refactorings in preperation for #564 (Filter anti features)
requested to merge pserwylo/fdroidclient:issue-564--filter-anti-features--refactor-and-test-in-prep into master
As described in #564 (closed), there is a small amount of ground work to be done in order to support a UI for filtering anti features. This is the first stage of that. A subsequent MR will add a database migration to put anti features in their own table, and have a join table between apps and anti features. See commit messages for more detailed descriptions.