One route exam

Every part of the exam is now available from one url instead of 6.
Removed a lot of duplicate code and potentially slow redirect chains.
Better Messages.
Sign out option

Added links to all public exam views that allows the user to sign out
if they are signed in as the wrong person.
Better Test Taker entity

Stopped using a generic 'vars' field to hold answers, points, and start
and end times, made it record the datetime of every status change, and
allows for multiple people to grade a test (outputs the average).
Bug fixes
Merge pull request #14 from dmhurley/exam-improve-branch

Exam improve branch