Add back drawing of custom bounding polygons

[Kovoschiz]

While dragging rectangles was much needed, hand-drawing irregular polygons are still useful. The polygon found from searching the location don't always work either. Or it could be an arbitrary area or linear corridor that needs to be investigated, for some changesets or objects. Unrelated but I don't feel like opening another new issue yet: In the future, the addition of a circle-drawing mode could be explored for finding changesets within a distance (radius) of the center position, as demonstrated in Terra Draw. Alternatively, drawing a rectangle by dragging from its center point ("center rectangle" in Solidworks term, in contrast to "corner rectangle") can be added, but I can't understand if this is available from them.

[Pseudorandom-Pseudonym]

This could be useful for loading changesets via a tasking manager; complex task areas currently seem to use a quadrilateral bounding box.