Compute port's side based on position and get rid off PortItemBase.side.

[zuckerruebe]

When, e.g., laying out a connection we rely on the relevant ports' side property. For this to work, keeping side up to date arcoss rotating, mirroring and loading a block item needs to be doen correctly. It not always is, plus it's annoying to have to do it.

Instead, I propose a port's side should be computed on the fly (based on its original position and the block item's transform).