[V3 Config] Add MongoDB driver (#972)

* Basic Mongo Driver

* Update docstrings

* WIP motor support

* Use motor

* Update docs, add selective importer

* Make use of selective importer

* Fix docs

* Fix config storage location for JSON

* Add delimiters in the drivers doc section

* Make async things async

* Add basic config information for mongo driver

* get info from basic setup into config

* IT WORKS

* Add dependency for RJM's PR.

setup.py

@@ -106,7 +106,7 @@ setup(
     ],
     extras_require={
         'test': ['pytest>=3', 'pytest-asyncio'],
-        'mongo': ['pymongo', 'motor'],
+        'mongo': ['motor'],
         'docs': ['sphinx', 'sphinxcontrib-asyncio', 'sphinx_rtd_theme'],
         'voice': ['PyNaCl']
     }