A lot of changes:

-Add 2 attributes to syringefilled : throughput (boolean to kwow if we
work with vol/duration or vol/trhoughput) and update_remaining_volume (a boolean to know when we have to update the remaining volume
-Fix conversions methods of syringe_filled
-fix start_exchange method of syringe_filled
-add graphical interface for the two new attributes
-add a ne button to load syringe database