#1 Student permission to access exam

[Daniel Santamaria]

1. students only having access when they're entitled to

when setting up students for an exam, should also
specify the time which the exam is valid for. of course
this is optional.

2. students only having access *where* they're entitled to

specify a range of IP addresses which are acceptable.
Have to look more into this.

3. access being stopped

account locking/unlocking functionality