Resolve RAP-253 "Add sol flagging"

This MR adds support for flagging of calibration solutions. Extreme amplitude solutions are identified and flagged, and these flags are then transferred to the phase solutions. The fraction of flagged solutions is now recorded in the main log. Many changes were needed to support flagged solutions in functions that deal with combining solution tables (in scripts/combine_h5parms.py) and smoothing of solutions (in scripts/process_slow_gains.py). The LOESS smoothing was found to work incorrectly with flagged solutions and was replaced by smoothing based on LoSoTo's smooth operation.