Refactor maps

[rouille]

Map are becoming more and more complex displaying on a single canvas transmission lines (AC and DC), generators, upgrades, soon storage, etc. We need to refactor the way we build the maps such that we can easily add layers (transmission, generator, LMP with color bar, etc.) instead of having a function that does one, the other or a combination of two.

A good design would be to have a user facing function as we have right now, e.g., map_lmp but internal to that function, we have successive calls to other function, e.g.,:

canvas = plot_canvas(canvas_kwargs)
canvas = add_states(canvas, state_kwargs)
canvas = add_lmp(canvas, scenario, lmp_kwargs)
return canvas

So if the user just wants to map LMP, there is a convenience function (map_lmp), but if they want to add LMP to an existing map that have let's say transmission map on it, the user can use the add_lmp function