Unify the naming "settlement" vs "collaborative close"

[klochowicz]

There is a mixture of the 2 spread around the codebase, spreading needless confusion. Let's pick one of the 2 and roll it out (preferrably at a time when there's no hure PRs in-flight :) )

Any preference?

[thomaseizinger]

With #741 in mind, my vote goes down for "settlement" because then we have two fairly distinct names for the two different kinds of closing which I think is good. Features that work completely differently should have different names.