Rename SelectionMode enum values

rename MULTIPLE_INTERVAL_SELECTION to MULTIPLE, SINGLE_SELECTION to SINGLE
Justification: less typing and horizontal 'cost' for developers, as well as one less 'selection' reference, which is already very heavy.

For example:
listView.getSelectionModel().setSelectionMode(SelectionMode.MULTIPLE_INTERVAL_SELECTION)
becomes
listView.getSelectionModel().setSelectionMode(SelectionMode.MULTIPLE)