Migrated Rake test annotation_category_test to RSpec.

Created rspec tests for the AnnotationCategory model.
I'm not 100% sure what we are trying to change here? Other then to add a little more guarantee that only a single record was created.

I have changed it from ` expect(@initial_size).not_to eq(AnnotationCategory.all.size)` to `expect(@initial_size + 1).to eq(AnnotationCategory.all.size)`.