Partially implements FS#180 - Inconsistent naming - special status of

saturation. In particular, it deals with the capitalized "S"-function in
the material laws:
Sgr -> sgr
Snr -> snr
SnToSne -> snToSne
Sreg -> sreg
Sw -> sw
SwToSwe -> swToSwe
SweToSw_ -> sweToSw_
Swr -> swr
Swrx -> swrx

Reviewed by Christoph. 



git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@10757 2fb0f335-1f38-0410-981e-8018bf24f1b0