Converted csettle() to use real/SimdReal template
The csettle() routine for constraining coordinates has been converted
to call a template function that is instantiated with either real or
SimdReal. On Haswell this makes settle a factor 5 faster.
Added reorganized indices to the SETTLE data structure, these are set
by a new function settle_set_constraints analogous to LINCS.
Reorganized the SETTLE initialization.
The settle fatal error no longer report the atom index of (one of the)
problematic water molecule, but the pdb dumps are more useful anyhow.
Change-Id: I61d81ad8a0add6fe234f8c7b5b44dc8c7084ace9