fix attendance_record uniqueness validation

In an attempt to refactor the original solution for this, we instead
broke it. We didn't know because we didn't test it after 5. I am
officially deeming this the gremlin bug, because it only show up
after midnight (utc). This commit kills the gremlin, so all is
right in the world.
Merge pull request #32 from epicodus/fix-time-issues

fix attendance_record uniqueness validation
add assessment model, routes, controller, and specs
add validations to assessment model
add assessment requirement model, update associations
rename assessment_requirement model to requirement -- cherry picked
display submissions
merge grades
add association between user and grade
adjust relationships surrounding assessments

Before grades served as a join between an assessment and a requirement
to give a score for the one requirement on a submission. This groups
grades together into a review, allowing us to have a note that isn't
tied to a specific grade, as well as a user who did the reviewing.
create index view for assessments
remove authorization from submission controller
allow user to view and submit an assessment
remove uneeded routes for submissions
add method to tell if a user has made a submission for an assessment
fix name of assessment_pages_spec
have assessment show page show different information depending on if the user's submission state
style assessment show page
add timestamps to submission model
refactor assessments pages specs to be more readable and better reflect the expected behavior of the assessment show page