mouse-over pop-up message causing unexpected window resize

[regel]

@stormpython the pop-up message when we mouse over a given value is very helpful but sometimes we cannot read the text at all. Pop-up text is always displayed on the right. When we mouse-over a tile that is already on the right of the heatmap, the pop-up will be printed outside visible window boundaries causing Kibana to resize the window.

A nice enhancement would be to calculate pop-up position according to the mouse-over tile position and window size to avoid the above UX.

kibana 4.5.4
https://github.com/stormpython/heatmap/archive/1.0.0.zip