Reload qxscan_params from previous scan

[gfabbris]

The parameters are all saved in the baseline, something like:

In [23]: cat[-1].baseline.read()["qxscan_setup_edge_Estart"]
Out[23]: 
<xarray.DataArray 'qxscan_setup_edge_Estart' (time: 2)>
array([-12., -12.])
Coordinates:
  * time     (time) float64 1.633e+09 1.633e+09
Attributes:
    object:   qxscan_setup