issue #312 - moved getTitle(), removeTitle(), setTitle(titleText) for grid group to one place

I have moved the getTitle(), removeTitle(), setTitle(titleText) for grid group to one place.
I put a if statement to check if the child node of the grid is a group. If so, it defines the three methods accordingly. If the titleText is null or empty, the set method will remove the title.
Tested on both ripple and device. It works well.