Look API Changes for Leaderboards

[kkartunov]

Look API has undergone dev changes which demand updates in the frontend. The ticket implements what is needed to support the renamed API fields.

For now, only TCO21 dev leaderboard is switched to the new format which results in issues https://tco21.topcoder.com/competition-overview/development/leaderboard.

Testing page: https://community-app.topcoder-dev.com/__community__/tco21/competition-overview/development/leaderboard

[SathyaJayabal]

@kkartunov , looks good except for one user's avatar