Update existing GCP icons using updated official GCP icons:
see https://cloud.google.com/icons. This includes changes to GCP nodes
and examples shown on the website.
Note, generic icons are updated with the corresponding new generic icon,
except "ai-platform-data-labeling-service.png" since it now has its
own unique icon.
Closes#554.
refactor
David Dansby
Pierre-Yves Aillet
