Keep up with coffea histogram changes

[areinsvo]

In coffea 0.6.7, the usage of project() and group() was changed and our plotting code is no longer compatible. Our code needs to be updated. The current plotting code should still work with coffea 0.6.6 but breaks in 0.6.7.

From the cms-coffea-users egroup:
Just an FYI, coffea 0.6.7 introduced two backwards-incompatible changes to the histogram interface:

• Change Hist.group() signature to be consistent with Hist.rebin()
  To upgrade: transpose the two arguments: Hist.group(new_axis, old_axis, ...) to Hist.group(old_axis, new_axis, ...)
  (per Different interfaces for hist.rebin() and hist.group() scikit-hep/coffea#90 )
• Rename hist.project() to hist.integrate()
  Currently hist.project() will perform the same action as before, but emits a FutureWarning that it will eventually change behavior. In the meantime, just replace calls to project() with calls to integrate(). The signature is identical.