Remove oppressive terminology in SCA

[Natalia Bidart]

In the lp:software-center-agent project there are a number of terms that we should replace.

1- snap's allow/block countries (currently known as whitelist/blacklist)
2- snap's public metrics block list (currently known as public_metrics_blacklist)
3- store's store inclusion list (currently known as store_whitelist)

There are a few non trivial changes to coordinate with clients and dependent services:

- Item (2) is used from the storefront (can be changed easily, with coordination with Luke).
- Items (1) and (2) are pushed from SCA to snapident.
- Item (3) is pushed from SCA to snapident's 'stores/%s/whitelist' % store_id

Besides the above, the changes on DB columns names would mean a short outage on (snap) publisher APIs.