Merge pull request #273 in PIPE/pipeline from PIPE-657-theoretical-thermal-noise-rms to master
* commit '94e5d69316440a8cd07cde12cff166b31b23598a': PIPE-657: a minor change to use rasterutil.gap_gen PIPE-657: Improvements to error handling in calculate_theoretical_image_rms PIPE-657: use of effective BW instead of nominal channel width PIPE-657: Some fixes for dec correction, multi-MS, absolute-OFF, or multi-sources. PIPE-657 initial round of implementation of theoretical thermal noise of images.
