Clean-up towards a continuous deployment model

"Continuous deployment model: The code on the master branch is always tested and deployable.  Any testing that needs to happen should be done on the feature branch before it's merged into master."

Now we have a conversion for `geom_bar` but we should support more aesthetics than just `fill` (http://docs.ggplot2.org/current/geom_bar.html).  Also, line 231 of `ggplotly.R` should be moved outside the for loop.  Then we will be able to check off `geom_bar` in this list: issue #18 :)