BUG: rank is always unranked

[Jackywathy]

the get_rank based on rank_id is incomplete. It currently returns UNRANKED. We should try to fix this up before release. Unfortunately missed this before sending the earlier pull request.

need to somehow differentiate between old style vs new style ranks (since ubi changed the rank system). This is currently done by hard coding each season's ranks in season.py (possible enhancement in the future could be to consolidate this into just two).

• implement get_rank(rank_id) to return the rank corresponding to that rank id
• add rank definitions for earlier seasons
• ensure rank works for each season (commit this as a example file so we can test this in the future)

[Jackywathy]

@billy-yoyo probably best not to release till this is fixed - should be pretty simple though.