Revise test matrix

[bsipocz]

There has been some update in upstream versions since the latest matrix revision, e.g.

• we should tests with Python 3.7

• there are quite a few untested numpy combinations, too that can be spread over the matrix.

• Also, changing the numpy dev testing to be with python3 I feel would make much sense.

• One of the python3 egg tests can be dropped.

• codestyle check to be moved up to the initial tests, if we are failing a build with it, it should be done sooner rather than later to avoid wasting too much CI resources

[bmorris3]

I think most/all of these points have been addressed since this issue was posted, most recently via #493.