Add openmw + dependencies

postmarketOS cannot be all serious and no fun, so this MR adds one of the best games ever. It requires a keyboard/mouse to play, and the Morrowind proprietary data files.. but my motivation behind doing this work is that some devices (librem5) will support 'docking' to an external display + keyboard/mouse. It's worth noting that there is an Android port of OpenMW that does support touch screen (and works really well TBH), maybe that can be looked at later so all devices can have some fun.

I plan to try and upstream this to Alpine, so if it doesn't make sense to add this to pmaports in the interim we can close this MR.