Interpolate colour selection circle

On the character select screen, after choosing a character, your collected spray cans (plus the character's default colour) are shown in a spinny circle for you to choose a colour. This merge request interpolates that colour circle's rotation.

When pressing "Default", the shake animation might appear slightly wilder now, but also smoother and shakier, as it's interpolated back and forth (i.e. across the middle, "moving" much more) instead of "teleporting" from side to side once per tic.
(On that note, is it intentional that the shake animation's strength is based on how few colours you have? With two colours, the shake is +/- 180 degrees, whereas with eight colours, the shake is +/- 45 degrees.)

[Click to expand game spoilers]

This also interpolates the costume, follower-category, follower, and follower-colour circles.

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TL;DR: Improved interpolation