Use css flexbox to resize viewport, instead of watching gridwidth and gridheight

Grid resize is very slow, and it doesn't give a good image to people using the grid. A way to reduce a lot of overload by removing watches is to change all resize logic to css flexbox by replacing most/all ng-style tags (very slow). This change will also help to activate again the scrollbars.AUTO flag which is the best option for scrollbars (as it removes the need of coding this checking on ui-grid controllers).