git-gui: Better document our blame variables
The array variable "order" used to be used to tell us in what
order each commit was received in. Recent changes have removed
that need for an ordering and the "order" array is now just a
boolean 'do we have that commit yet' flag.
The colors were moved to fields, so they appear inside of the
blame viewer instance. This keeps two different concurrently
running blame viewers from stepping on each other's ordering
of the colors in group_colors.
Most of the other fields were moved around a little bit so
that they are organized by major category and value lifespan.
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>