do not delete jobs when a worker return an error
return a empty list of repo revisions always
use logger instead of print for logging messages
get render configuration file from server using http request

Some times on worker side is not possible to have a shared render_settings folder and this means that this settings will not be available for rendering jobs. This is solved by sending the content of config file to the worker and save hem in a temporary file for render time usage.
sign worker to poweroff when no more jobs are available

* in some situations when you need to go to rest and there remain only a few shots to render, Brender can automatically power-off all workers that were signed as "shutdown at the end"
report render status after any frame

* this commit introduce a major modification, it enable brender to receive report from blender after any rendered frame. in this way we save few more things like rendered time and output path for files.
* ability to restart only frame with errors and not chunks
* ability to download a frame for local preview ... no thumbnail for now