Search: Option to filter out forms

[magical]

Requested on IRC, sorta.

eevee, it'd be nice if you'd add a feature to the Pokémon search that toggles display of megas
so that if I'm doing an oldgen search (say, 1-4), I don't see any megas in it
since megas are gen 6

This use case would be better served by a generation slider, but it still might be useful to be able to filter out forms in general (especially once we get rid of the distinction between functional and aesthetic forms).

[magical]

Been playing LeafGreen recently and the lack of this has been annoying me.