MaMuT_: initialize brightness dialog after launchPanel() so that the panel JFrame is already present
(The panel is used as the owner of the brightness dialog)
MaMuT_: add new spot feature SOURCE_ID that identifies the view from which a spot was added.
MaMuT_: fix javadoc
MaMuT_: set SOURCE_ID feature when creating a spot.
MaMuT_: minor clean up