Allows selection of the interpreter and commandline parameters.

Also add support for ".pyqtc" as a project file, containing
a flat list of .py files, similar to the Generic Project.

Change-Id: If75a0affd735223a658ce7fce0d010ebf49695f2
Reviewed-by: hjk <hjk@theqtcompany.com>
Reviewed-by: Nikita Baryshnikov <nib952051@gmail.com>
Reviewed-by: Christian Stenger <christian.stenger@theqtcompany.com>