Added Ghost and GhostNorm functions to ColorSpinorField

These return pointers to the ghost data for QUDA_PARITY_SITE_SUBSET fields.
They generate an error for QUDA_FULL_SITE_SUBSET fields since the ghost
data for different parities are not contiguous in that case.
Also moved void *v and void *norm into ColorSpinorField from the derived
classes. Updated the constructors accordingly.
Merge branch 'master' of github.com:lattice/quda