Add cursor offset

[robob27]

Stonesense allows you to follow the DF camera and specify an offset by using direction keys. This works really well and allows me to see the parts that I think I should see in Stonesense based on what I can see in DF. However, when I activate a cursor in DF, stonesense will jump way off from where it seems like it should display.

Here are some screenshots to demonstrate what I mean:

In the above screenshots, when a cursor is not active in DF, the offset makes stonesense display what I would like it to display. Now if I activate a cursor in this spot without shifting the map:

It seems like the offset is applied from the cursor position, which puts my view out into oblivion. It would be cool if you could specify a second offset that would apply only when the cursor is active, so I could have my follow+no cursor offset be -40,0,0 while my follow+cursor offset would be 0,0,0, which displays what I expect stonesense to display with the cursor active:

Alternatively, having a toggle that would not apply the offset when a cursor is active seems like it would also solve this. Presumably this works properly as is for people with certain setups/window sizes etc.

[robob27]

Removing https://github.com/DFHack/stonesense/blob/2908625499accc4899e9a9f0e999c95be26ce14d/GUI.cpp#L464 locally seems to give the desired effect at least with my configuration.