Only apply rotation in Globe projection

Flat projections don't render rotation, but it was possible
to change it with right-click drag and break mouse navigation.

This fixes issue, where in flat projection map movement may not match mouse input while panning. There are two ways to reproduce:

A.

1. Open Marble
2. Select Globe projection
3. Right-click rotate 90deg, so Earth's rotation axis lies horizontally
4. Select Mercator projection

Now X-Y axes are swapped while panning.

B.

1. Open Marble
2. Select Mercator projection
3. Right click drag over approx. half map's view-port

Now map and mouse movement is misaligned while panning.