TNL-930: Turn off Student Notes when Harvard Annotation Tool is enabled.

Disables Student Notes if one of `textannotation`, `imageannotation`, `videoannotation` modules exist in the list of `Advanced Modules`.

There is still possibility to break `Student Notes` and `Harvard Annotation Tool`:
  - add one of `textannotation`, `imageannotation`, `videoannotation` to the `Advanced Modules` list;
  - add one of `textannotation`, `imageannotation`, `videoannotation` to the unit;
  - remove it form the `Advanced Modules` list => **You can enable Student Notes now. If you have both modules in the sequential, it breaks one of these modules.**

I think we should write a good note about this situation.

@tymofij , @olmar, @jmclaus, @srpearce  please review.

**sandbox:** http://studio.polesye.m.sandbox.edx.org/
According to the PMs, Harvard is the only school that has access to the Harvard annotation tool. I'm concerned that people who see it mentioned here will start asking about the tool and wanting to use it - so I think this message should go directly from PMs to Harvard instead of appearing to all of our worldwide users in Studio.

Also, can the display name be "Enable Student Notes," since that's what we've been calling this feature?

Assuming we can change the display name and we don't want to mention any other annotation tools in the UI, I'd revise this text to just the following:

Enable Student Notes
Enter true or false. If true, students can use the Student Notes feature.