pa() should identify reflections used to compute UB

[prjemian]

The reports that list the orientation reflections should clearly identify which reflections (and in which order) have been used to compute the UB matrix.

Thanks @rodolakis for the recommendation!

[prjemian]

One change is to provide a standard call to get the orientation reflections. Currently, this list is provided by libhkl.

(bluesky_2021_2) mintadmin@mint-vm:~/.../Bluesky/hklpy$ git grep reflections_get
examples/tst_UB_in_stream.ipynb:    "    reflections = self.calc.sample._sample.reflections_get()\n",
hkl/diffract.py:            for i, ref in enumerate(sample._sample.reflections_get()):
hkl/sample.py:        return [refl.hkl_get() for refl in self._sample.reflections_get()]
hkl/sample.py:            r1 = self._sample.reflections_get()[-1]
hkl/sample.py:            refl = self._sample.reflections_get()[index]
hkl/sample.py:        reflections = self._sample.reflections_get()
hkl/sample.py:        refl = sample.reflections_get()
hkl/sample.py:        refls = self._sample.reflections_get()

[prjemian]

This should done with other work on reflections, such as #158 and #178, for the v1.1 release milestone.

[prjemian]

===================== ====================================================================
term                  value                                                               
===================== ====================================================================
diffractometer        fourc                                                               
geometry              E4CV                                                                
class                 SimulatedE4CV                                                       
energy (keV)          8.05092                                                             
wavelength (angstrom) 1.54000                                                             
calc engine           hkl                                                                 
mode                  bissector                                                           
positions             ===== =======                                                       
                      name  value                                                         
                      ===== =======                                                       
                      omega 0.00000                                                       
                      chi   0.00000                                                       
                      phi   0.00000                                                       
                      tth   0.00000                                                       
                      ===== =======                                                       
constraints           ===== ========= ========== ===== ====                               
                      axis  low_limit high_limit value fit                                
                      ===== ========= ========== ===== ====                               
                      omega -180.0    180.0      0.0   True                               
                      chi   -180.0    180.0      0.0   True                               
                      phi   -180.0    180.0      0.0   True                               
                      tth   -180.0    180.0      0.0   True                               
                      ===== ========= ========== ===== ====                               
sample: main          ================ ===================================================
                      term             value                                              
                      ================ ===================================================
                      unit cell edges  a=1.54, b=1.54, c=1.54                             
                      unit cell angles alpha=90.0, beta=90.0, gamma=90.0                  
                      [U]              [[1. 0. 0.]                                        
                                        [0. 1. 0.]                                        
                                        [0. 0. 1.]]                                       
                      [UB]             [[ 4.07999046e+00 -2.49827363e-16 -2.49827363e-16] 
                                        [ 0.00000000e+00  4.07999046e+00 -2.49827363e-16] 
                                        [ 0.00000000e+00  0.00000000e+00  4.07999046e+00]]
                      ================ ===================================================
===================== ====================================================================