Comment and grade directly on the code

[gmuraru]

It depends on #163.
Having the possibility to view the source code directly in the browser, the teaching assistant should now be able to add comments on specific lines (specify cases of bad indentation, parts of the code which they liked, etc.) from the code.
By adding comments like:

+1.0: Nice idea

The student should receive 1.0 bonus points to the grade.

-1.0: Did not check the returned value

The student should receive a 1.0 penalty to the grade.