Blender Git Loki

Fix: Drivers popover not showing

This was broken since cca87ccc753a85b447872a259c9d3e3f07ec1c13

The problem was that as this popover was defined in the C-code
for the Graph Editor, the relevant panel never got added to the
WM_paneltype registry, since only Python defined panels get
WM_paneltype_add() called when they are defined.

Since the majority of panels defined for regions are only used there,
a more localised fix was applied here by only adding the driver popover
to the global list manually.