Refactored gpu part in core module.

OpenGL API changes:

• Removed ogl::Texture2D support from Input/Output arrays (it doesn't have Mat-like interface).
• Added Stream support to ogl::Buffer.

GPU API changes:

• Added CudaMem support to Input/Output arrays.
• Renamed gpu headers (all headers now starts with gpu_ prefix).
• Refactored GpuMat interface (switch to Input/Output arrays, added Stream support).
• Refactored CudaMem interface (now alloc type can be changed only via constructor).
• Fixed Stream interface (problems with casting to bool).
• Refactored gpu info structures (now DeviceInfo provides full information about device from cudaDeviceProp).
• Added Event class (wrapper for cudaEvent).