Add coloring modes to the blame page (issue-2, pull request #125)

Blame output is now colored according to Commit (default), Author or
Age. Both Commit and Author output uses random colors whereas Age uses a
single color with varying tints applied to indicate the age.  White
indicates the eldest commit with the tint darkening as the commits get
younger.

Change-Id: I045458329af4765e91d5829ce3e8d28e21eeb66e