Adapt to new header keywords for hexapod positions

Data from LAM now uses new header keywords for the hexapod positions that we want to capture in the butler.

	Float(name='X', invalid="NaN", units="mm", FITS=('W_ENFCAX', 'ENU_FCA_FOCUS')),
	Float(name='Y', invalid="NaN", units="mm", FITS=('W_ENFCAY', 'ENU_FCA_SHIFT')),
	Float(name='Z', invalid="NaN", units="mm", FITS=('W_ENFCAZ', 'ENU_FCA_DITHER')),

Note that the x,y,z coordinate convention is that of the hexapod, so that:

• "z" is the shift along the slit (spatial dimension).
• "y" is the shift perpendicular to the slit (spectral dimension).
• "x" is focus.