Functional CASA-uvmcmcfit

No more miriad dependency!!

Also, switched to .fits format for posteriorpdf.
Interactive cleaning is optional

Non-interactive cleaning is a bit faster.
Convert to YAML configuration file format.
Bugfixes

Reflecting changes introduced with the adoption of config.yaml.
Preliminary attempt to merge CASA branch into master.
Accept CASA or uvfits files.

Also update visualutil.py to accommodate yaml configuration files.