Added colored bar charts, along with a test

This commit cleans up the bar chart update logic, adds support for
using a lookup table to map an array to colors for the bars. It also
adds a test verifying the points, and the bars, using C++, and the
same array/lookup table.

Change-Id: I11585739f5a0c5bca3240274aebafead302e89ec
Merge topic 'plot-bar-lut' into master

b2e4fb38 Added colored bar charts, along with a test