Enable an otherwise nonexistant pan mode in the UI. (fixes #2)

Thanks to @ryancnelson for the tip. (makerbot/ReplicatorG#284)
The logic was setting ROTATE_VIEW for *everything* unconditionally,
this changes it such that:

* on a mac, when shift is held down and a mouse1 drag happens, it sets TRANSLATE_VIEW
* on a !mac, when a button3 drag happens, it sets TRANSLATE_VIEW.

src/replicatorg/app/ui/modeling/Tool.java

@@ -36,7 +36,7 @@ public AxisControl(String title, JPanel parent, double initial) {
  if (Tool.this instanceof ChangeListener) {
  spinner.addChangeListener((ChangeListener)Tool.this);
  }
- } 
+ }
  }
 
  public JButton createToolButton(String text, String iconPath) {
@@ -58,20 +58,20 @@ public CoordinateControl(JPanel parent, Point3d coordinate) {
  axes[1] = new AxisControl("Y",parent, coordinate.y);
  axes[2] = new AxisControl("Z",parent, coordinate.z);
  }
- 
+
  public void update() {
  axes[0].model.setValue(new Double(coordinate.x));
  axes[1].model.setValue(new Double(coordinate.y));
  axes[2].model.setValue(new Double(coordinate.z));
  }
  }
- 
+
  abstract String getTitle();
  abstract String getButtonName();
  abstract Icon getButtonIcon();
  abstract String getInstructions();
  abstract JPanel getControls();
- 
+
  final protected ToolPanel parent;
  public Tool(ToolPanel parent) {
  this.parent = parent;
@@ -83,13 +83,13 @@ public Tool(ToolPanel parent) {
  public void mouseDragged(MouseEvent e) {
  if (startPoint == null) return;
  Point p = e.getPoint();
- DragMode mode = DragMode.ROTATE_VIEW; 
+ DragMode mode = DragMode.ROTATE_VIEW;
  if (Base.isMacOS()) {
  if (button == MouseEvent.BUTTON1 && !e.isShiftDown()) { mode = DragMode.ROTATE_VIEW; }
- else if (button == MouseEvent.BUTTON1 && e.isShiftDown()) { mode = DragMode.ROTATE_VIEW; }
+ else if (button == MouseEvent.BUTTON1 && e.isShiftDown()) { mode = DragMode.TRANSLATE_VIEW; }
  } else {
  if (button == MouseEvent.BUTTON1) { mode = DragMode.ROTATE_VIEW; }
- else if (button == MouseEvent.BUTTON3) { mode = DragMode.ROTATE_VIEW; }
+ else if (button == MouseEvent.BUTTON3) { mode = DragMode.TRANSLATE_VIEW; }
  }
  double xd = (double)(p.x - startPoint.x);
  double yd = (double)(p.y - startPoint.y);