Merge branch 'diagonal-spring-rings-tweak' into 'next'

Diagonal spring rings tweak

If you didn't know before, those special placement ring lines for diagonal springs only use multiples of 45 for their angles in-game. In other words, they only face any of the 8 basic cardinal directions (N, S, E, W, NE, NW, etc). Considering that springs themselves don't follow the above behaviour, you can probably work out that's a bad thing.

This branch changes that of course, if you couldn't guess from context. Diagonal spring rings can now be placed with any angles like most thing types already could!

See merge request !37