Connect frequency data to GraphView

Now the button presses result in a new graph being drawn.
One problem is that on the start up screen, an empty graph
doesn't get drawn, and that has to be fixed.

The labels for the graph aren't clear (not all the numbers
are shown).
Fix graph vertical labels

Earlier they were printing float values; now this is fixed
so that they only print integers.

Signed-off-by: Prashant Malani <p.malani@gmail.com>