Alter CELL-related saveframes from Recorded to Derived

[rowlesmr]

will close #439

With moving CELL from EXPTL to DIFFRN, the related parameters should no longer be Recorded.

[jamesrhester]

I don't think the move between categories of itself changes the _type.source, rather it is whether or not the values can be derived from other quantities that have data names defined. I suspect the original classification of Recorded might have been a leftover from the days when reflections were measured separately on a point detector, from which cell parameters where calculated and then used to position the gonio for each hkl. The items going into that cell parameter calculation were not necessarily captured by CIF. Anyway, happy for these to be derived, as you could argue that the contributing reflections are listed in DIFFRN_ORIENT_REFLN.