graphlog: make node symbol templatable by ui.graphnodetemplate option
New ui.graphnodetemplate option allows us to colorize a node symbol by phase
or branch,
[ui]
graphnodetemplate = {label('graphnode.{phase}', graphnode)}
[color]
graphnode.draft = yellow bold
or use a variety of unicode emoji characters, and so on. (You'll need less-481
to display non-BMP unicode character.)
[ui]
graphnodetemplate = {ifeq(obsolete, 'stable', graphnode, '\xf0\x9f\x92\xa9')}