Corrected how filters are indexed

Was indexing on how filters are annotated (e.g. potentially
Filter.class) instead of their concrete type, resulting in constantly
overwriting filters.

Corrected to now index on the actual class.
MinMaxFilter: annotate on Filter.class

Now annotating on type = Filter.class instead of MinMaxFilter.class.
Merge branch 'annotation-fixes'

Fixes issues with how filters annotations are processed and indexed.

Now indexed on the actual filter class, and not the plugin type.