Improve sub-screen rendering

[fabio-t]

• allow chaining of screens? Eg, if you [t]hrow, but don't have a wielded weapon, we should open the inventory screen and after a weapon is selected go forward with the Look screen. If ESC is pushed we go back to play screen. Instead of keeping a single field with the next screen, we should instead have a list. If we don't go through with that, the list is purged.

• subscreens should not cover the whole screen, but adapt to the size of their content

• they should also have a nice border, possibly not just white (a nice purple maybe?)