Describe the pull request

This PR improves command buffers to allow for some boilerplate code to be removed from application implementations:

• Staging buffers can now be avoided by directly mapping memory through an extended ICommandBuffer::transfer overload.
• It is now possible to bind multiple descriptor sets at once using a new ICommandBuffer::bind overload. This can even be advantageous for Vulkan descriptor sets, if they are in a contiguous range, as this allows the engine to bind them through a single command (although the effect is probably minimal).
• Barriers can now be created from command buffers.