Enhanced the RangeEditor with end labels

Added a new 'label_width' facet to the RangeEditor which allows labels
indicating the range bounds to be added to the ends of the RangeEditor.
Added 'change_mode' to Grid/PropertySheet editors

Added a new 'change_mode' to the grid and property sheet adapters which
allows controlling when changes made in a cell editor are applied to the
underlying model.
Enhanced float editing in ListViewEditor

Added a 'float_editor' facet to the ListViewItem to allow modifying the
default editor used when editing float values.