support/scripts/graph-build-time: add download times

support/scripts/graph-build-time: add download times

Total build time also involves download. Getting a visibility on the impact
of that step can be important for users/admins, e.g. to evaluate different
methods of BR2_PRIMARY_SITE.

Colors used are some kind of purple (primary scheme) and light orange
(alternate scheme).

Signed-off-by: Mathias De Maré <mathias.de_mare@nokia.com>
[ThomasDS: rebase and update colors to avoid confusion]
Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
Tested-by: Matthew Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>