Fix field AssessmentPart.criterion to point to Criterion table.

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

TNL-826
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
Merge pull request #638 from edx/muzaffar/tnl58-date-validations

More accurate validation for date & time in studio editor.
TNL-62, TNL-72 and TNL-811
Merge pull request #633 from edx/ammar/tnl72

TNL-72 & TNL-62 & TNL-811
Merge pull request #634 from edx/usman/tnl826-assessment-part-criterion-foreign-key

Fix field AssessmentPart.criterion to point to Criterion table.
Code refactoring after PR code review.

TNL-814
Merging master into this branch
Code refactoring after PR code review.

TNL-814
Minor code refactoring.

TNL-814
Merge pull request #636 from edx/muzaffar/tnl814-multiline-issue-ux

fixed the multi-line issue for criterion prompt, criterion option text,
Imported and configured bi-app sass module for rtl support.

TNL-813
Replaced direction related css properties with mixins from bi-app-sass.

TNL-813
Added single-box-shadow sass mixin with rtl support.

TNL-813
Flip fontawesome's icon-caret-right 180deg in rtl.

TNL-813