FLECS Style UI creation

[Kubic-C]

Further development of the UI design, im pushing this off later to go work on the primary focus of the engine which would be tiles.

To get to the point: allow a FLECS style creation of a UI element.

The reason I want to add this is it would simplify creation of UI elements, and reduce boiler plate. (PS i hate boiler plate)

example below

// this will make the element display in the middle of the screen
canvas->add_text("hello_world").add_horizontal_constraint(SPK_MIDDLE).add_vertical_constraint(SPK_MIDDLE);