* Change unapproved and unconfirmed account to not be accessible in the REST API
* Change Account#searchable? to reject unconfirmed and unapproved users
* Disable search for unapproved and unconfirmed users in Account.search_for
* Disable search for unapproved and unconfirmed users in Account.advanced_search_for
* Remove unconfirmed and unapproved accounts from Account.searchable scope
* Prevent mentions to unapproved/unconfirmed accounts
* Fix some old tests for Account.advanced_search_for
* Add some Account.advanced_search_for tests for existing behaviors
* Add some tests for Account.search_for
* Add Account.advanced_search_for tests unconfirmed and unapproved accounts
* Add Account.searchable tests
* Fix Account.without_unapproved scope potentially messing with previously-applied scopes
* Allow lookup of unconfirmed/unapproved accounts through /api/v1/accounts/lookup
This is so that the API can still be used to check whether an username is free
to use.