Fixed some bugs in mixed evaluation relating to self-evaluation

Firstly, I have fixed some checkstyle errors from the last commit

I have also slightly modified export pdf inComplete/unEnrolled
list generator. The code is now checking whether the list contains
any ids first before grabbing the users' names. This way it solves
the bug that sometimes return names of users that are not even
in the group. I have also slightly modified mixed evaluation to
accomodate the possibility of having empty sections. For example,
having peer-evaluation questions but were filtered out with one of
the available filters.

Fixed saving self-evaluation questions bug if the evalutor is not
asked to evaluate themselves with peer-evaluation questions.

Removed ScoreDropdown questions from the Self-Evaluation section
because it doesn't make sense to distribute marks to only one person
(eg. evaluator).

Changed the student mixed evaluation results view to auto display
self-evaluation results similar in rubrics where the evaluator's
submission is displayed whether the results are released or not.
Therefore no release buttons are required for self-evaluation results.
Modified sytem tests for mixed evaluation

I have modified student_mixeval to include some of the changes
to id and class names due to the addition of the self-evaluation
section.

I have added tests for adding, editing, and reordering self-evaluation
questions in add_mixeval system tests.
Modified student mixed evaluation's system test

I have modified the tests to include tests of filling out the
self-evaluation questions and their results. I've also tested
that self-evaluation results are auto-released and self-evaluations
are not available for tutors.
Modified the logo to be a link to the home page.

Previously, the logo is just an image in the top left hand corner.
I have now modified it to also be a link that goes to the home
page of the application.