Allow for filtering on 'taxonomies' on the overview pages.

[bobdenotter]

It even works with paging, and it 'sticks' when using 'save and return to overview'. ^_^

See screenshot:

[GwendolenLynch]

Key "taxonomy" for array with keys "name, singular_name, fields, default_status, 
show_on_dashboard, searchable, viewless, slug, singular_slug, show_in_menu, 
sort, groups" does not exist in "overview/_panel-actions_overview.twig" at line 24

[Pinpickle]

🎉

[GwendolenLynch]

Changing to this passes acceptance tests:

{% for taxonomy in context.contenttype.taxonomy|default([]) %}

[GwendolenLynch]

It just fell in there, all on it's own!

[bobdenotter]

Ha, was I taking too long? ;-)

[GwendolenLynch]

I needed a sanity break, and figured you were having a busy-as-hell type of day.