GUI: new pattern cursor logic, part 1 - READ

this new pattern cursor logic will finally allow you to click on any
cell of the previous/next pattern and take you there
on top of that you'll be able to make selections that go beyond the
boundaries of a pattern

operations are not supported yet, so don't try it out!
it won't work properly until I adapt the code.

src/gui/gui.cpp

@@ -8609,9 +8609,13 @@ FurnaceGUI::FurnaceGUI():
   wheelX(0),
   wheelY(0),
   dragSourceX(0),
+  dragSourceXFine(0),
   dragSourceY(0),
+  dragSourceOrder(0),
   dragDestinationX(0),
+  dragDestinationXFine(0),
   dragDestinationY(0),
+  dragDestinationOrder(0),
   oldBeat(-1),
   oldBar(-1),
   curGroove(-1),