Add play parameter to Slots/Slotted Edge

[florianfesti]

As noted in https://hackaday.io/project/10649-boxespy/discussion-176555 slots don't do well with tight fits. There needs to be an option to make them wider without changing the burn value.

This is not 100% straight forward as the SlottedEdge cuts a few corners like not having a Settings class and abusing the settings parameter for the section length. This needs to be clean up first.