Checked for NumberFormatException when handling node ID filtering. This
really only happens with test topology data.
Minor cleanup in selection listener calls.
Changed SavedHistory to store vertex selection state. Changed topology
classes so that the SelectionManager is contained inside the
GraphContainer. This makes sense because the GraphContainer represents
the current session-specific data for the UI and the current selection
is part of the session-specific data. Fixes bug SPC-562.