Added handles to the xFormModifier. There's a control in the
GUI to disable them if you use more than one modifier on an object. The handles are only shown if the item it's attached to is actually selected. Individual handles may be turned off using the buttons on the top left of the viewport, these also allow for opening the graph editor with the respective envelopes. The buttons are a bit finicky and require a slight mouse movement to register the click (this is a LW issue).