Cleanup mongodb authentication

Authenticate to the database before getting a reference to the
collection.
Defined baseUrl in the LMS template, fixing a bug where HTML editors called within LMS would fail to load
Merge pull request #1258 from edx/flowerhack/fix/htmleditor

Defined baseUrl in the LMS template
Disabled video caption acceptance tests
Merge pull request #1261 from edx/will/disable-caption-tests

Disabled video caption acceptance tests
Merge pull request #1229 from rocha/cleanup-eventtracking-mongo-authentication

Cleanup mongodb authentication