Add a link to the instructor dash in the course staff debug info

In anticipation of using the analytics infrastructure to put ORA2 data CSV files in the instructor dash, this PR adds a link to the instructor dash to the ORA2 staff debug information.  This will allow instructors to more easily find where to download this information.

@cpennington Is it safe to use course IDs in the instructor dash URL like this?
```
courses/{{ COURSE ID }}/instructor#view-analytics
```
Right now, I'm getting the course ID from the XBlock scope IDs and using `to_deprecated_string()`, but this could change in the future depending on what we need to do to support split mongo.

@stephensanchez Please review.