Explicity tracking author of a remark ...

The author of a 'sandboxed' remark could be / would be different from
the author of the 'live' remark. Hence, the author should be tracked
explicitly
 Added some basic query methods
Defined the concept of 'live' for Examiners ...

A 'live' examiner is one who has passed the mentorship program and can
now be given work for grading

This is a different concept from an 'active' account in that an
'active' account allows one to log-in. The 'live' field only
determines what an Examiner is allowed to do once logged-in
 temp commit before removal
Stylistic changes
Defined activate & deactive methods for models ...

Makes sense only for models that have an associated account.
Moreover, for examiners, also changes the :live field as needed
Added methods to get apprentices and mentors

Applicable only to models with an associated account
Moved code for viewing fdb to core/

Previously, only students and teachers could see feedback.
But now, the same mentor-apprenticeship relationship can
exist between two examiners. And the mentor examiner might want
to see how the apprentice examiner grades papers.

It makes sense, therefore, to re-use the same infrastructure as before
[Sandbox]: Temp commit

Too much code to be left uncommitted
[Sandbox] Tieing up lose ends in the first draft of sandboxing capability