v0.7.4

Branding fixes and Premier ratings.

- Player and team banners that were the wrong shape are now centre-cropped to fit instead of being refused. Any banner upload used to fail unless the image happened to be near 4:1, which is why no player had managed to save one.
- Team logos and banners can be removed, and a team's branding can be set by URL as well as by upload. Owners and league admins can edit both.
- Super-admins can take down a player's avatar or banner and a team's logo or banner.
- Team season stats now use each player's CS2 Premier rating (the latest rating-history entry) instead of the internal 1500 default, so a team of two players at 14,000 and 22,000 no longer shows as 1500 / 1500 / 3000.

Pull request: https://github.com/mtottenh/cg/pull/17