BN-33 Adding composing support

[rabits]

Become a quite huge change after testing on clouds, which show inconsistency in the BlendNet logic:

• Added compositing support (for now executed on Manager will be moved to Agent by [FEATURE] Move compositing operations from Manager to Agent #65)
• Now engines (Manager & Agent) are init provider overrides after TaskExecutorBase to use its configs
• Added more debugging information
• Changed defaults for create workspace and run blender script - there is no defaults anymore, you need to provide data into.
• Run blender script now accepts the blend file to make sure it will be loaded before the script running (important on small systems)
• Fixed issue with saving the one-layer render (instead of multilayer exr) on small systems
• Improved the error reporting - now it's more clear for user
• Fixed issue with using instance id instead of name in the resources list on the Manager
• Added isstopped logic to the ManagerAgentWorker to properly remove it when the Manager instance will go down later
• Changed the Manager render merge policy - now it's executed once when all the samples for the task are prepared
• Fixed the error with not stopping the ERROR task on Manager (no way to run another task after error task)
• Slightly improved saving the tasks mechanims - it should not cause deadlocks anymore
• Added local provider saving the added agents
• Addon: It's downloading results in async mode
• Addon: It's saving the compose result in place of the frame, previews saved to temp folder and available only during preview and render (if requested) is saved to the render directory with name of task.

fixes: #33