Multi-GPU support - dev version (unstable-v0.16.0-rc1)

Development version of Multi-GPU feature, allows Provider to offer multiple GPUs from single computer.
Build introduces new Offer specification of GPU resources. Currently format isn't supported by SDKs.

Image can be downloaded from: https://repo-golem-gpu-live.s3.amazonaws.com/images/golem-gpu-live-unstable-v0.16.0-64.img.xz