Extract Validation Logic

[natalynyu]

This PR makes our validation code a bit more modular by extracting the error related interfaces from the CourseModal component into a common directory as well as some logic handling bad request error messages.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] I have run eslint on the code
• [x] I have added JSDoc for all of my code (where applicable)
• [ ] I have added tests to cover my changes.

Priority:

• [x] Normal
• [ ] High

Related Issues:

Fixes #348

[codecov[bot]]

Codecov Report

Merging #635 (8454770) into develop (c7a9b1b) will increase coverage by 0.00%. The diff coverage is 100.00%.

:exclamation: Current head 8454770 differs from pull request most recent head 5b4a46f. Consider uploading reports for the commit 5b4a46f to get more accurate results

@@           Coverage Diff            @@
##           develop     #635   +/-   ##
========================================
  Coverage    95.11%   95.11%           
========================================
  Files          192      193    +1     
  Lines         4484     4487    +3     
  Branches       543      544    +1     
========================================
+ Hits          4265     4268    +3     
  Misses         102      102           
  Partials       117      117           

Impacted Files	Coverage Δ
...ent/components/pages/RoomAdmin/CreateRoomModal.tsx	93.00% <ø> (ø)
...lient/components/pages/RoomAdmin/EditRoomModal.tsx	89.55% <ø> (ø)
src/client/classes/Validation.ts	100.00% <100.00%> (ø)
src/client/classes/index.ts	100.00% <100.00%> (ø)
src/client/components/App.tsx	96.66% <100.00%> (+0.11%)	:arrow_up:
...rc/client/components/pages/Courses/CourseModal.tsx	86.73% <100.00%> (-1.01%)	:arrow_down:
...lient/components/pages/Courses/EnrollmentModal.tsx	88.05% <100.00%> (-0.68%)	:arrow_down:
src/client/components/pages/Courses/NotesModal.tsx	89.09% <100.00%> (-0.39%)	:arrow_down:

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