refs #8639. Separate make transmission corr function

Separate make transmission corr function. Utilised by existing transcorr function, but external facing. If not all arguments provided, pick them out of the IDF.
refs #8639. Refactor out hard-coded stitching values.

This has been a long-standing problem, but is easily fixed now.
Merge remote-tracking branch 'origin/feature/8639_trans_corr_quick'