Pass through a known good `Context` to `translateCategories`

All the good work to make sure that getActivity() actually returned a proper context, obtaining a final reference to that known good activity object, and then using that in the background thread is thrown away. The reason was because the translateCategories method would go and call getActivity() all over again. This changes the translateCategories helper function so that it asks for a Context. This way, a known good Context can be passed in, rather than having to perform a check to see if getActivity() is good again.

Fixes #603 (closed) (Hopefully)