Added step to generate delay calibration solution files

This MR addresses RAP-167. The step produces an h5 solution file from the input MS.

This step requires local copies of facet_selfcal and lofar_helpers, and requires the paths to these copies to be supplied as the input parameters selfcal and h5merger, respectively. Note that facet_selfcal above is a fork of lofar_facet_selfcal with LOFARBeam removed. The former will be replaced by the latter in the future.

Furthermore, facet_selfcal requires a configuration file facetselfcal_config.txt that should be supplied as the input parameter configfile. An example configuration file is supplied with this MR.

There are some caveats when operating the pipeline with delay_solve. The concatenation steps earlier in the pipeline introduce flags, which don't play well with the internal working of facet_selfcal. It is therefore important that the steps of the pipeline must be run without concatenation. This issue will be addressed in RAP-243.