Bubble visualization for splits on 2 dimensions

[beibm]

one split for X axis, second for Y axis, just like highcharts bubble chart

[mkuthan]

I think we should start with heatmap visualization #212 when the measure value is presented by colour (or gradient) instead of bubble diameter. Cell colours (or gradients) will be described using legends, like in line charts.

[adrianmroz]

bubble charts or better scatterplot would work better if we have categorical data as points and axis with continuous measures. We first need to figure out how we could define this in turnilo UI.