#27 Fix wheel scrolling on LiveGrid content (on Firefox)

[Joey Schulze]

This bug report is for the rico3 branch (Bug: Cannot be selected in Milestone select).
In Rico3 LiveGrid this.tabs consists of 3 elements, not of 2 as in Rico2. Thus the handleWheel function is not connected with the content part of the LiveGrid.
Additionally, scroll delta defaults to 0 and is not adjusted when running Firefox (since e.detail is missing).
The attached patch takes care of both.