Ability to select points from multiple lasso selections

[dpdiliberto]

This is a feature request to provide the ability to select points from multiple lasso selections. It would be helpful to be able to:

1. first lasso a group of points,
2. use the lasso feature a second time to lasso a different group of points in a separate part of the map, and
3. still have both groups highlighted.

It can currently be challenging to lasso points in separate areas on the map.