Fixed lo_arg pointer bug in mapper_msg_prepare_params()
Swig/Python: Fixed string pointer bugs in py_to_prop()
Added function mdev_properties(), also call it from Swig/Python bindings.
Changed arguments to mapper_monitor_connection_modify() for consistency with mapper_monitor_connect() and _disconnect(). Altered coresponding function name in Swig/Python bindings from .modify() to .modify_connection() since other objects e.g. links can be modified also.
Updated test.py for testing device properties and link/connect/modify.