Add button to unlock new Inscription slots

[Dekar]

Add a button next to the Prodigies button that lets you get an inscription slot for category point, so that all uses for cat points are accessible on one screen.
It also indirectly shows new players that you can do this, something that is not obvious so far.

[Dougiegee]

Very good idea. I think it takes most new plays a long time to work out that they can buy a slot.

[darkgod]

done