Fix a typo in if condition used to show thrive articles.
  - It was showing them only for the Design track.
  - Articles will be shown for all tracks except for the Design track.

References #4765

fix(challenge-detail): condition for showing thrive articles

Fix `challenge.status` at conditional check.
The status property of a completed challenge was `COMPLETED` before,
it's `Completed` anymore.

fix(submission-management): missing `Add Submission` button

fix(submission-management): add null checking for `currentPhase`

Issue: #4752

Issues: #4752 #4765 #4755 #4758

fix: for issue #4756

This reverts commit bf0c810.