Beautify cmake file
Continue fixing picongpu cmake file

 - add PIC_VT_ROOT_DIR variable
 - remove .s
 - remove sm_13 and check for unsupported compute capab.
Update other cmake files
Fix CUDA_NVCC_FLAGS in cmake file
Merge pull request #79 from f-schmitt-zih/pretty-cmake

Beautify cmake file

- fix nvcc_tmp dir