Some improvements to dicom conversion

-Added support for more types of MLCs (Siemens 58 and 82), and separated
the leaf handling code to its own method for more flexibility.
-Made the #to_dcm method restore the DICOM loggers level to its previous
level after type conversion is complete.
-Improved the case where a Site setup is missing, so that the conversion
to DICOM will complete in this case, but give a warning about the
missing isocenter position.