Non-CUDA modules compile without linking CUDA library

In previous commit - 73d46f8d88, every module was linked using CUDA library.
Linking an unnecessary library is useless. Moreover, in that case, running the module requires the CUDA library on the system (not setup in most environments).
Check, Python-side, if the user has a CUDA-capable GPU

Code sample:
  In [1]: from menpo.cuda.tools import is_cuda_available
  In [2]: is_cuda_available()
  Out[2]: True

The check calls a CUDA-module, menpo.cuda.cutools, that is responsible to check whether or not the user has a compatible GPU.

This call can fail in two cases:
  1) the user uses binaries compiled without nvcc - he does not have CUDA binaries
  2) the user does not have libcudart.so on its machine
in both cases, he cannot run CUDA code.