Support for scatter plots

[mattloose]

I don't think this plugin correctly supports scatter plots - as with heat maps it appears to only output a subset of the data.

[TorsteinHonsi]

Can you demonstrate that? Here's a scatter plot: http://jsfiddle.net/highcharts/cqjvD/894/

[personman]

I'd like to try to improve it a bit. There are no labels in the current version. And if you have multiple series, the layout seems kind of strange. I made an attempt at a new version of the scatter and bubble exporter. Here's my pull request: #66

[TorsteinHonsi]

Duplicate of #49 - two points with the same X values are not supported.