Servicex

This is really a RC - we think this is the final set

- Uses API tokens to work with ServiceX
- Defaults to no image name - which means that you end up using the default in ServiceX
- Add `ignore_cache` to allow one to ignore the current cache when submitting a query.

- Do not close the root file when we load a lazy array from it. The LazyArray requires things to be open.

A few bug fixes:

- Default developer end-points should work if there is no `.servicex` file present
- Combining files from the uproot backend to awkward arrays should now work.

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

This time on the right branch!

This is a bogus release and is identical to 2.0!