Clamp ZLayer between -1 and -24 to avoid UI issues

In KSP the background of the tech tree is at layer 0. Inversely,
for nodes to be ABOVE it they need to have a ZLayer of lower than 0.
However, the UI (Sidebar etc..) is at -25, so puttina node at ZLayer
lower than -24 will make it show above the UI.

Fix #29
Extend workspace slightly

Still needs to be properly matched with KSP
Bumped to v0.2.1