Enabling Cell selection on mobile browsers

Adding the touchend event to the row selection event, so that selection works on mobile browsers. This is a fix for Issue https://github.com/angular-ui/ng-grid/issues/1759
Similar in nature to these fixes 
http://stackoverflow.com/a/3303834/888165 
https://github.com/angular-ui/ng-grid/commit/4bb2d6996aad6463155bcd01b1521441cab45270 for Issue https://github.com/angular-ui/ng-grid/issues/1551
Merge pull request #1901 from vargose/patch-1

Enabling Cell selection on mobile browsers