scrollbars can be enabled per instance (horizontal or vertical)
and have the options: NEVER,ALWAYS,WHEN_NEEDED those er in
uiGridConstants.scrollbars.XXXX
the horizontal scrollbar should not fall oout of the view
we also don't do that for the vertical scrollbar, 
If the ng-grid is places in a container that doesn't allow overflow then
the horizontal will never be shown..
Merge pull request #2009 from Servoy/scrollbars2

scrollbars can be enabled per instance in 3 modes: always,never or when_needed