Add "rarity-from-introduced" checklist status

[Adam Winer]

For example, vagrant Eurasian Collared-Doves in US/CA states/provinces where they are review species currently get listed as “rarity”, but that means that sightings are properly assigned “introduced” status.

[Adam Winer]

Infrastructure in place with commit 060b316af. Still need to go through all the species with both introduced and rarity status somewhere.

[Adam Winer]

Resolve Issue #456: Add "rarity-from-introduced" checklist status

Finnished going through every species with both "rarity" and "introduced" status. Also found a Gibraltar checklist, and a smattering of very sketchy records that needed to be removed.

→ <<cset ba38b7056256>>