Miscellaneous selfcal improvements
This MR makes a number of improvements and fixes to selfcal that were identified as part of RAP-197 (testing on multiple fields). The changes include:
- adjustments to the normalization of amplitude solutions. Two new parameters were added to the strategy to control the way normalization is done
- the
solve_min_uv_lambda
parameter was moved from the parset to the strategy, to allow it to vary with selfcal cycle - the default calibrator target fluxes were reduced and the default maximum number of directions was increased for each cycle
- the number of sources found in the image was added to the selfcal convergence criteria, as it is sensitive to the overall image quality in ways the other criteria (median noise and dynamic range) may not be.
Fixes were also made to the sky model filtering step (to improve stability and speed) and to the MPI imaging mode (which was broken).