Update flutter data model + new admin features

[neketka]

Summary

This pull request updates the flutter data model to retrieve the latest changes from the server. Achievements are now editable form the admin frontend. We also have some useful new features like duplication and moving on admin frontend.

• Automatic refresh of events on flutter side
• Achievement admin page
• Change challenge completed logic + new challenge logic to accomodate existing player
• Achievement tracker updates
• Connect achievement trackers to frontend

Test Plan

All journeys load as usual.

[dti-github-bot]

[diff-counting] Significant lines: 1383. This diff might be too big! Developer leads are invited to review the code.

[cathli66]

Resolved all issues (talked through in person and on Slack). Achievements are fully working, so are real time event updates on the flutter side.

Only thing that doesn't work yet is updating event trackers upon adding a new challenge to an existing completed event. This isn't really necessary for internal launch though and the other changes in this PR need to be merged in asap. We can continue working on this feature in a later PR.

[jasmineee-li]

The achievement tracking functions and logic for completeChallenge LGTM! I just finished some e2e tests for achievement tracker and tested -- they all run successfully. I added the tests to a new PR!