Graph color config

[lusingander]

[graph.color]
branches = [
  "#86ac41",
  "#7da3a1",
  "#34675c",
]
edge = "#324851"

[alerque]

Unrelated to the color scheme: the example graph in this PR looks unnecessarily complex for the info being presented. There are 10 crossing lines for 5 branches when it could be drawn in the same space with 0 crossing lines. Obviously the example is contrived and not all cases will have such a clean possibility, but it does look like the logic is backwards. There are two metrics going on that could be used to cleanup the graph: either the merge point or the date stamp of first commit in the branch. If either of those metrics was used to determine the innermost branch to draw and draw later merge points/later first commit dates farther out in the branch graph the resulting graph would have no overlaps at all and I think it would be much clearer at a glance what was going on.