Version 1.1.5 release

We're well overdue for a new release as there have been a number of bug fixes since the last one.

I've listed a few open MRs in here that I think we should get.

The final motivation for this release was !1054 (merged). However, this is really just a stopgap. astropy-v5 doesn't support python37 and other packages we use are slowly dropping support. I suggest that this is also a good opportunity for us to stop supporting that version? My proposal is for 1.1.5 to be the last release supporting that version. The next release would be 1.2.0 with no py37 support.

If this is the last py37 release, we should do our best to ensure that all of the open bug fixes are merged.

Thoughts? @gregory.ashton @sylvia.biscoveanu @matthew-pitkin @moritz.huebner