Text and Video Annotation Modules - First Iteration

The following code-change is the first iteration of the modules for
text and video annotation.

Installing Modules:
1. Under “Advanced Settings”, add “textannotation” and
“videoannotation” to the list of advanced_modules.
2. Add link to an external storage for annotations under
“annotation_storage_url”
3. Add the secret token for talking with said storage under
“annotation_token_secret”

Using Modules
1. When creating  new unit, you can find Text and Video annotation
modules under “Advanced” component
2. Make sure you have either Text or Video in one unit, but not both.
3. Annotations are only allowed on Live/Public version and not Studio.