Behavior of zooming via mouse wheel

[alex-w]

Original report: https://bugs.launchpad.net/stellarium/+bug/1207979

Could you make zoom with the mouse wheel at the point where the mouse cursor like in Google Maps?

Short explanation from question: If I want to zoom in on a star that is located in the upper left now before I have to center it on the screen and then zoom in, zoom with google style simply position the mouse cursor and zoom in on the star, it is more immediate, more simple.

[axd1967]

To remember: even better is an option to enable/disable this "cursor zoom".

This way, users can choose between the current and the proposed behaviour.

An alternative to a setting is to use ALT(or some other combination)+scroll to zoom to the cursor position.

The reason is that pointing is critical and should not be influenced by a random mouse movement.