Func-adl-servicex

Certify this works with python 3.8. No code changes, but setup files needed their meta-data updated.

Added support for python 3.6.

First release of ServiceX `func_adl` frontend code.

- Use either `ServiceXSourceUpROOT` or `ServiceXSourceXAOD` to access the two types of backends.
- Make sure your `.servicex` file is in the proper location and contains tokens for the backends you want to use

Splits the xAOD and Uproot interfaces

Hopefully this will go!