Update docstrings of the public API
Remove refresh_keys

Never should be done a bulk upload of keys. The updating of the keys
should not be a task for the user of the keymanager. Keys will be updated
by the keymanager in a background worker one per one.
Pass the cipher_algo to the encrypt wrapper
Remove get_key_from_cache

We only need to cache the fetch with a sort timeout. The tests that
fetches keys now have to use different keys or will be cached.
Rename method get_all_keys_in_local_db -> get_all_keys
Remove parse_openpgp_ascii_key

Don't fit with the logic of the keymanager and it's not use except for
some commented code in bitmask_client
Add changes
Merge remote-tracking branch 'meskio/feature/cleanup_api' into develop
Implement 'fetch_key' for ascii keys

binary keys support is still missing