Windows build and OpenCL/Cuda host code unification

[atillack]

This PR adds functionality to build an OpenCL Windows version using VisualStudio. Additionally, to make future expansions a bit easier, I merged the OpenCL and Cuda host source (performdocking.h/cpp).

In order to do this the new windows/ directory contains OpenCL headers and link lib files with compatible licenses from Khronos - license files are included.

This PR also bumps the base version up to v1.6 (Windows builds will be labeled already with it) for us to slowly gear up towards a new release ... 70+ commits do deserve a bump to v1.6 ;-)

Please test extensively. Although there should be no algorithmic changes the code reshuffling needs full tests for both Cuda and OpenCL to verify.