Added public method to reset the grids selection.
Realized that selectCells() will already reset selection when called without parameters
Made row based selection more consistent

Made row based selection (especially when shift selecting) more consistent. (Used the behaviour of the Thunderbird list as reference).
Removed console.log used for testing
Merge pull request #117 from ckosmowski/feature-rowselection

More consistent shift click behaviour for rowBasedSelection.