Schema changes for checklist translation

This is an extract of commits from the checklist_translation branch, which cover:
* adding new translation columns to ranks & change types
* adding functionality in the S+ admin panel to manage ranks & change types translations
* adding functionality in the S+ admin panel to set is_current on CitesCop events
* adding import scripts to populate translations of: ranks, change_types, Cites regions, hash annotations
* adding import script to populate CoP start dates 

This does not include changes to materialized views or serializers.

`rake db:migrate`
`rake import:checklist_translations`
`rake import:cites_cops_start_dates`

+ go to CoPs and set the last CoP as current, so that we don't forget to do that later.

Smoke checks to perform:
* taxon concept auto complete (S+, Checklist, Cites Trade)
* Checklist pdf downloads
* geo entities list api call (S+, Checklist, CitesTrade)