Updated body background color to match gtk

Background color in the webkit widget now matches the gtk theme.
Added gtk.Treeview to display random data in gtk

The data that is displayed in the graph is also available in a
gtk.Treeview to verify that what is being plotted is what is expected.
Added scrolled window to the data treeview

With the current window size the treeview doesn't display the whole
dataset. Hence, a scrolled window has been added to wrap it.

Also, the other widgets in the vertical box no longer expand since the
treeview is the only widget that takes advantage of this.
Increased main window height to display dataset

With the previous size only the colum headers were displayed.
Added a few classes to make svg more readable

Groups now have class attribute to make svg more readable when looking
at it with the browser