Feature/cleanup api

Depends on: https://github.com/leapcode/leap_mail/pull/152
Interrelated with: https://github.com/leapcode/bitmask_client/pull/756 & https://github.com/leapcode/leap_pycommon/pull/92

_I'm not sure if commits should be rebased together_
This method is still used in bitmask_client and soledad:
https://github.com/leapcode/bitmask_client/blob/develop/src/leap/bitmask/backend/components.py#L917
https://github.com/leapcode/soledad/blob/develop/scripts/profiling/mail/mail.py#L34