* heatmap: fix converting error when series contains 0 and log scale is selected, issue #8884
* heatmap: fix app crash when Y min set to 0 with log scale
* heatmap: fix tooltip for 'zero' buckets in log scale
* heatmap: fix tooltip histogram for log scales
* heatmap: fix flicker of the highlighted element
this was caused by too often fired mouseenter/mouseleave events
* heatmap: fix missing X axis option for log scales
* heatmap: fix missing zero bucket in tooltip histogram
* graph: initial histogram support #600
* graph histogram mode: add Bars number option
* graph histogram mode: fix X axis ticks calculation
* graph histogram mode: change bar style (align and width)
* refactor(graph): move histogram functions into separate module
* graph histogram mode: rename series to "count"
* graph histogram mode: fix errors if no data
* refactor(graph and heatmap): move shared code into app/core
* graph: add tests for histogram mode
