Heatmap chart visualization

[stormpython]

Adds a heatmap chart visualization to core Kibana. The functionality for this visualization is based on the heatmap plugin.

The purpose of this visualization is to compare large datasets on 3 axes, the column and row dimensions as well as the color (value) dimension.

The heatmap visualization allows you to select

1. Date Histogram aggregation
2. Histogram aggregation
3. Range aggregation
4. Date Range aggregation
5. IPv4 Range aggregation
6. Terms aggregation
7. Filters aggregation
8. Significant Terms aggregation

along 2 different axes - Columns and Rows.

The color of each cell represents the metric aggregation.

Display Options

Color Scales
The heatmap uses Cynthia Brewer Color Scales.

Color Range represents the number of colors in the Color Palette.

Margins
Allows users to increase or decrease the margins around the heatmap chart.

Padding
Adds padding to each cell of a heatmap matrix.

Stroke Options
Allows users to add a stroke color to heatmap cells as well as increase the size of the stroke-width.

Axis Options
Allows users to filter axis labels.

Legend Number Format
Allows users to specify the format of numbers in the legend.

number (Default)

[stormpython]

@thomasneirynck I've signed the CLA so I am not sure why the check isn't working. Perhaps it needs to be run again.

[elasticmachine]

Can one of the admins verify this patch?

[stormpython]

That seems to have done it.

[thomasneirynck]

cf. #1265.

[thomasneirynck]

Adopting this. Let's try and pull this over the line as well. For working version on latest master, check(https://github.com/thomasneirynck/kibana/tree/enh/heatmap).

[thomasneirynck]

I added the blocked label. We're going to pull this over the line, but likely take a different approach. The refactors in #9044 are extracting XY charts as a separate core class in the vislib. @ppisljar did a POC, and Heatmaps are suitable to be a specific implementation of that.

[epixa]

Replaced by #9403