Optimize the performance with the multi-tasking

[hermet]

Try threading optimization with the nested web workers if the perf. can be increased.

• Suggested Model1:

launch the next commands on 2 web-worker.

picture->load() / canvas->push(picture) / picture->update(picture)

canvas->draw()

• Suggested Model2:

launch the next commands on one web-worker.

picture->load()
canvas->push(picture) or picture->update(picture)
canvas->draw()