Feature/time wheel

NOQE 

Still need to write tests and such (and move the example to a reasonable place), but want to get initial feedback from the plottable team.
Can we rename the x / y scales here?  I'm not too familiar with wheel charts unfortunately but my initial understanding is that there is not really a concept of x and y since it is a radial type of plot.  Can we use a different attribute name so that it is more evident what information the wheelPlot is presenting