Add get_courses() to mongo modulestore

* Note: This doesn't run yet
* add config file for lms on mongo
* Some comment additions and cleanups

lms/envs/dev_mongo.py

@@ -0,0 +1,16 @@
+"""
+This config file runs the dev environment, but with mongo as the datastore
+"""
+from .dev import *
+
+MODULESTORE = {
+    'default': {
+        'ENGINE': 'xmodule.modulestore.mongo.MongoModuleStore',
+        'OPTIONS': {
+            'default_class': 'xmodule.raw_module.RawDescriptor',
+            'host': 'localhost',
+            'db': 'xmodule',
+            'collection': 'modulestore',
+        }
+    }
+}