Add gall should have region select

[Megachile]

Now that we're global, there are lots of cases where galls occur in a native range and hosts have been widely planted elsewhere. Our default assumption within NA has been that anywhere the gall occurs, the host might occur as well. But globally, I think we should default to the opposite: the galler is restricted to its host's continent of origin. EG Pediaspis aceris is on several maples planted ubiquitously in NA but the range map shouldn't imply the wasp is likely present there. So if we had a region select on the gall page it would prefilter the range easily to deselect any places where the host occurs but the gall isn't known to yet.

[jeffdc]

If there are multiple hosts would this region filter eliminate all of them? It gets very confusing very quickly if you have multiple hosts and several of them are introduced. We have info on native/non-native range when we pull from WCVP. What if we stored this information and tracked non-native ranges? Then when it comes time to edit a gall's range we can separate out the non-native range and let the admin decide if we should include it or not.