Allow text wrapping in WPF controls

Added the ability to wrap text by calling DiffView.EnableTextWrapping(). This addresses issue #113

I approached this issue by creating a Boolean value(IsTextWrapEnabled) that keeps track if the text should be wrapped or not(If DiffViewer. ToggleTextWrapping() is called).
If !IsTextWrapEnabled then the Add() method would simply create a StackPanel with horizontal Orientation, which does not allow text wrapping.
However if IsTextWrapEnabled the Add() method would create a WrapPanel instead with the same orientation as StackPanel, which does allow text wrapping.
I did some styling modifications for the scenario that text wraps to make sure that number,operation,text variables align within the DiffViewer.
To further ensure text would wrap, if IsTextWrapEnabled then we would set the Horizontal scroll bar visibility to hidden/disabled

mmanela / diffplex