Address keywords in datamodels but missing from the keyword dictionary

[braingram]

At the moment these are:
HDU: COMBINE1D KEYWORD: SOURCEID
HDU: COMBINE1D KEYWORD: SPORDER
HDU: COMBINE1D KEYWORD: SRCTYPE
HDU: EXTRACT1D KEYWORD: DISPAXIS
HDU: EXTRACT1D KEYWORD: EXTRXSTP
HDU: EXTRACT1D KEYWORD: EXTRXSTR
HDU: EXTRACT1D KEYWORD: EXTRYSTP
HDU: EXTRACT1D KEYWORD: EXTRYSTR
HDU: EXTRACT1D KEYWORD: INT_NUM
HDU: EXTRACT1D KEYWORD: MJD-AVG
HDU: EXTRACT1D KEYWORD: MJD-BEG
HDU: EXTRACT1D KEYWORD: MJD-END
HDU: EXTRACT1D KEYWORD: SHUTSTA
HDU: EXTRACT1D KEYWORD: SLITID
HDU: EXTRACT1D KEYWORD: SOURCEID
HDU: EXTRACT1D KEYWORD: SPORDER
HDU: EXTRACT1D KEYWORD: SRCALIAS
HDU: EXTRACT1D KEYWORD: SRCDEC
HDU: EXTRACT1D KEYWORD: SRCNAME
HDU: EXTRACT1D KEYWORD: SRCRA
HDU: EXTRACT1D KEYWORD: SRCXPOS
HDU: EXTRACT1D KEYWORD: SRCYPOS
HDU: EXTRACT1D KEYWORD: STLARITY
HDU: EXTRACT1D KEYWORD: TDB-BEG
HDU: EXTRACT1D KEYWORD: TDB-END
HDU: EXTRACT1D KEYWORD: TDB-MID
HDU: EXTRACT1D KEYWORD: TIMESYS
HDU: EXTRACT1D KEYWORD: TIMEUNIT
HDU: FGS CENTROID PACKET KEYWORD: DETECTID #340
HDU: FGS CENTROID PACKET KEYWORD: GUIDESTA #340
HDU: FLIGHT REFERENCE STARS KEYWORD: NUMREFST #340
HDU: PRIMARY KEYWORD: DITH_DEC
HDU: PRIMARY KEYWORD: DITH_RA
HDU: PRIMARY KEYWORD: KERNXSZ
HDU: PRIMARY KEYWORD: KERNYSZ
HDU: PRIMARY KEYWORD: S_MIREMI
HDU: PRIMARY KEYWORD: THRSPRC
HDU: SCI KEYWORD: SMOOTH_L
HDU: WCS-TABLE KEYWORD: TDIM2
(as reported by the tool added in #337 and against a modified keyword dictionary that fixes most of the oifits related differences).

This issue will be updated as the above are categorized.

These mostly look to be:

• extra extensions with names other than SCI (EXTRACT1D, COMBINE1D)
• GUIDESTA keyword definition refers to a HDU that doesn't match the keyword dictionary #340
• keywords that likely make sense to add to the keyword dictionary