:lipstick: Ignoring casapy log files
Refactored casa interface to be more functional

Can now iterate over casa data, before and after purification.
These iterators are used by the task to create images.
Cython functions are made to check for exceptions
Only ouputing real part of the image
Add option to iterate over data without scaling u and v

This is more for debugging purposes at this juncture.
add_dependencies does not work with files

It works with top-level targets. However, the dependency we were trying to add
should already exist.
Refactoring so casa and pyrap interface use same code

Goes towards #39 and #41
Can `python setup.py` install from any directory

Usefull when debugging.
Adding pyrap wrappers

- Closes #39 and  #41.
- Adds scripts for testing CASA and pyrap wrappers. Theses are not incorporated
  into the testing framework yet since we do not have data that is quite
  meaningfull yet and since getting the data into a measurement set requires
  having casapy accessible. It is not clear that we can even run get_data.py
  without user input.
- The pyrap testing scripts fails when writting the image, since it requires
  outside data that I don't know where to get.