Bubble charts

[wsw70]

This is a follow-up on #433 which was closed because the OP did not provide an example.

Would it be possible to support bubble charts which are 2D charts which allow to visually present a third dimension via the size of a bubble. An example would be this

from the following data:

[rashidkpc]

We actually have a plan for this and it isn't tough to implement. Its basically exactly the same as a line chart, except the dots have another metric agg attached to them that defines their size, and of course stroke width on the line would be set to 0.

You can expect to see this in Kibana 4.1