xspress3 support with the community IOC

[mrakitin]

We with @dmgav made the first pass with the community IOC ophyd classes from the nslsii package, and it worked with some manual preparation. Need to address the following items:

TODOs:

• Set up TTL Veto mode and number of points in the external trigger mode.
• Fix the shapes dynamically:

   xs.fluor.shape = (121, 8, 4096)
   xs.fluor.describe()
   Out[2]:
   {'fluor': {'source': 'SIM:fluor',
    'dtype': 'array',
    'shape': (121, 8, 4096),
    'external': 'FILESTORE:',
    'dtype_str': 'uint32',
    'dims': ('bin_count',)}}

• Sort out the wrong shape (251, 4, 4096) - it was related to the xs.fluor.name = "fluor" change. Without the change, it worked OK. We may still want to investigate where this change affects the shape change as PyXRF uses this fluor field for data access.

[mrakitin]

I think we can merge the PR. The CI issues are due to some unclear timeouts.