some changes to add tooltips.
Basically make sure that my modifications are not destroying the examples.
Add a div to make sure I can add the tooltip as seen here: http://techslides.com/demos/d3/d3-worldmap-boilerplate.html
This div should allow me to have several gantt charts per page.
one can specify the container for the tooltip and the D3 generated svg
removing some console.log
gantt-chart-d3.js: redraw modified to add the tooltips on the added bars, support multiple containers and keep compatibility with the original library.
examples/example2.js: modified to draw and redraw everything in container1
added some categories in the example just to have thiner lines...