Multipoints support

[Rub21]

cc . @willemarcel

[willemarcel]

@Rub21 amazing work. Some improvement suggestions:
Use a switcher to alternate between single and multipoint modes, something like this

I think we don't need two buttons for request items, we could have only one button and execute the action based on the active mode. If multipoint mode is active, request multi items, if single mode is active, request a single item. The button's label could be "Get geometries" or "Get masks".