* Add `from_account` to notifications API
this adds the ability to filter notifications by the account they
originated from
* passing a non-existent user should cause none to be returned
* Fix codeclimate warnings
* fix more codeclimate warnings
* make requested changes:
* use account id instead of user@domain
* name the param `account_id` instead of `from_account`
* Don't use `return` in a lambda
