Design and make docs for cursor image handling

[Insality]

Currently there is small integration with hover component and defos to manage the cursor images (like a different cursor image on button hover etc)

Need to design and make it flexible to use

[subsoap]

For reference a way of getting it to work currently to those who may search:

local button = self.druid:new_button("button/root", ...)
button.hover.style.ON_HOVER_CURSOR = defos.CURSOR_HAND
button.hover.style.ON_MOUSE_HOVER_CURSOR = defos.CURSOR_HAND

Reason for the two from chat

it's kind of old stuff with two hover things (first for touch handlers on mobile, other is for mouse hover with nil action)