Verify submission_uuid when creating assessments

This corrects an issue where assessments were sometimes incorrectly
associated with the wrong response.

The behavior was caused because the POST request to the `peer_assess`
handler only contained the feedback text/options and did _not_ include
mention of which original response was being assessed. If the current
workflow item is updated on the server _after_ the page first loads but
_before_ the page is submitted, this submission will be incorrectly
associated with the following response.

Steps to reproduce:
- Submit a response (User A).
- Wait for peers to submit responses (User B and User C).
- Load page with first peer response to be assessed (not not submit).
- Open the same page again in a new tab.
- In 1st tab, assess and submit assessment for User B.
- In 2nd tab, assess and submit assessment for User B.
- Notice that your assessment for User B's response is also applied to
  User C's response.

This changeset does _not_ restore data retroactively.

Fix TNL-680
Merge pull request #628 from stvstnfrd/uuid/verify-upstream

Verify submission_uuid when creating assessments
Created a Vagrantfile.
Updated README with instructions for setting up a Vagrant instance.
Make install-dev installs sass and python dev packages.
Fixed instructions for running workbench inside a vagrant instance.
Merge pull request #632 from edx/usman/add-vagrant-setup

Added vagrant setup.
Fixed syntax error in README.
Fixed criterion name with label which is displayed to the user.
TNL-768
Merge pull request #631 from edx/waheed/tnl768-fix-criterion-name

Fixed criterion name with label which is displayed to the user.
Fix field AssessmentPart.criterion to point to Criterion table.

Migration 0020 incorrectly altered the field to point to the
CriterionOption table.

TNL-826
Catch and log DatabaseErrors in assessment.api.self.create_assessment.

TNL-812
Added test for DatabaseError in assessment.api.self.create_assessment.

TNL-812
Merge pull request #635 from edx/usman/tnl812-catch-db-errors-in-api

Catch and log DatabaseErrors in assessment.api.self.create_assessment.
More accurate validation for date & time in studio editor.

TNL-58
Added email address to AUTHORS.
Using ISO_8601 for date formatting instead of string.

TNL-58
fixed the multi-line issue for criterion prompt, criterion option text,
peer assessment feedback and self assessment feedback.

TNL-814
Comment refactoring.

TNL-58
Adding more readable comments to catch block.

TNL-58