Remove debugging print commited by mistake
Don't graph null values
Fix bug when plotting categorical data in the y axis

This might be a bug with the tooltip plugin, or maybe the categories' one, I'm
not sure. Anyway, this solves the issue.
[#13] Add horizontal bars
[#13] Fix bar sorting with horizontal bars
Convert resource_view's show_legends to boolean
[#13] Fix bar width when plotting time in a horizontal chart