Pushing scaled visibility up in the call stack
parameters are set using scaled visibilities
Simplifies guessing of parameters
Remove file left over from 1e8b05b397d324192657b89f64697228f0814e04
:name_badge: Changing Measurement to Sensing
Expand types of objects that can function as visibilities

Used to be only dataframes. Should now work with sequences, dictionaries,
homogeneous numpy arrays and correctly names numpy records.
Remove dovirtualenv option since we don't use virtualenvs anymore
:lipstick: and :bug:s in error messages
:lipstick: trailing whitespace
:lipstick: Read long_description into variable rather than inline call
Adds casa task

Installation is done only if run from casapy.
Similarly, the task is imported into casa only if run from casapy.
The import is done when importing purify itself.