Support 9 piece frames

[ericoporto]

The idea is to add frame types and allow adding a 9 piece per frame type.

The frame could maybe use a 27 piece instead, being three 9 pieces on the side of each other, for normal, mouse over and mouse click.

A 9 piece could use a thickness parameter. The 9 piece is actually a 8 piece since may be a good idea to pickup the background from a different image

[ericoporto]

Found some interesting ui packs from Kenney, but I still don't know the interface to the ImGi :/

Some cool looking HD ui:
https://opengameart.org/content/ui-pack
https://opengameart.org/content/ui-pack-rpg-extension
https://opengameart.org/content/game-icons

And a pixel one:
https://opengameart.org/content/pixel-ui-pack-750-assets

[ericoporto]

Adding how it works in rpgmaker. I don't particularly think it's a good approach to have hardcoded sizes but this gives an idea of a way to store these graphics.

I think I will need to figure out everything that a theme needs eventually...

[ericoporto]

I think I need to add a draw_graphic command that has no tinting and has color be zero or alternatively repurpose the icon drawing, but make it skip tinting when color is zero