ServiceX front end package 2.1b1 release

Support multiple types of ServiceX backends implicitly

• The two types, xAOD and uproot are both supported in the sense they can return different types of data (root or parquet files)
• As long as you tell servicex what sort of file to expect, it can render the data into awkward arrays or pandas.DataFrame's.
• The interface and .servicex file have been update to support this, and also behave sensibly if the user doesn't specify anything.

Compatibility with ServiceX:

• Authentication framework will work only up to RC2
• Job submission, etc., should work accross most (all?) versions of ServiceX