Missing ctrl+Q keyboard shortcut to quit

Hi

Thanks @prabhuramachandran for your talk at scipy conference this year.

If I consider your first example

```import numpy as np
x, y = np.mgrid[-3:3:100j, -3:3:100j]
z = np.sin(x**2 + y**2)

from mayavi import mlab
mlab.surf(x, y, z)
```

The problem I'm facing is the impossibility to close the window. Some window managers (such as i3) control the windows only by key strokes. The top bar (reduce, maximize, close) never appears.
Usually, GUIs embed shortcuts like ctrl+Q to quit the apps.

Would it be possible to integrate that to mlab?

Thanks.