[UI - SierraVga] Text box skin

[persn]

Our current UI is just a black background with a white/gray foreground on it. We should look into making it better looking with actual graphics as backgrounds. Similar to the text box in the AGS prototype.

[persn]

I began work on this, but didn't get very far, my work may be useful in the future, in particular the sprites are all converted to png and is read to use https://github.com/persn/Hero6/tree/develop/feature/textbox-skin