python3 : ports missing a 37 variant

[BjarneDMat]

In order to be able to remove the python3[2-5] ports, py-{name} ports that are missing a py3[6-7]-{name} need to be updated -or- abandoned/removed.

Additionally, py-{name} ports that has a py36 version, but are missing a py37 version should indicate whether or not their port supports python37

Please indicate here -or- contact me directly regarding, what action you want to be taken, and I'll make a consolidated squashed and minimised pull.

See the "[portgroups] Python" thread in macports-user for further information/diskussion.