Change default Select interaction logic to select overlapping features

The original default behaviour of the Select interaction is to "Replace the currently selected feature(s) with the feature at the pixel". I made this code change to change the semantics to "Replace the currently selected feature(s) with the feature(s) at the pixel". I could not find a way to configure to get the desired behaviour with add/remove/toggle conditions).

This PR is a proposal with some unanswered questions and is built on #3018 as I was in need of both changes even though they are not dependant. Also, the "no change" condition was and is at fault since it only compares the first of the current selected features. I'm prepared to rework the PR if the questions can be resolved.

What is a sensible default behaviour? 

Should the default behaviour be configurable?