Improved Student class home page.

Students will only be able to select from problems sets with problems.
Implemented better way to check if a user is a student.
Whether a user is a student or instructor is now available in the
Session.
Merge pull request #62 from jwien001/master

Improved Student class home page.
Implemented adding new problems and sets.
Merge pull request #63 from jwien001/master

Implemented adding new problems and sets.
Fixed weird shit
Merge pull request #64 from sichinumi/master

Fixed weird shit
Student can now only solve unsolved problems.
Merge pull request #65 from jwien001/master

Students can now only solve unsolved problems.
Improved problem set search query.
Minor fix to SQL query.
Reworked retrieving sets for students.

Differentiated solved sets from locked and unlocked sets.
Updated student class home to display each set type in a separate
section.
Merge pull request #66 from jwien001/master

Database query improvements.