feature requests: Allow selecting and dragging multiple points.

[JackyHe398]

When I try to correct the points manually, I have to drag each point one by one. However, due to the nature of GPS errors, the offsets of nearby points are often similar in both direction and magnitude (for example, when the user is near a building, the error vectors usually point toward the building and have similar lengths).

Allowing users to select and move multiple points at once would greatly improve the correction process.

For example.

As you may see, the errors are tends to point towards a similar direction and magnitude. The red circle contains all the inaccurate points and I need to move all of them into the yellow circle. Without selecting multiple points, I need to drag tens of times to correct it.