add a draw() command & legend support
update test plots
add console.log statement so that notebook failure is explicit
BUG: fix undefined variable
FIX: use require.js where applicable
add test for custom plugin
update example notebook
BUG-FIX: the labels variable was wrongly overwritten when adding several PointLabelTooltip to a figure. Add extra test to detect the bug.
Merge pull request #39 from francisco-dlp/BUG-FIX_PointLabelTooltip_labels

BUG-FIX: PointLabelTooltip displays wrong when more than 1 plugin in fig
TST: test plotting with marker color equal to 'none'