filter on permissions should filter functions, not only categories

[cesar65]

Actual behaviour:
Filter on permissions only filters categories which have only functions without permissions in them. Functions without permissions in categories which also contain functions with permissions are not filtered.

Exptected behavoir:
All functions without permissions should be filtered regardless of the presence of permitted functions in the same category.

[M66B]

There is a small performance impact when filtering on permissions and drilling down categories.
I have minimized the impact by caching the filtered functions.