Gradient calculation, geometry optimization

Available for CCS, CC2, MP2, CCSD and CCSD(T) using integral direct analytic gradient.

For a single integral-direct gradient calculation:

**DALTON INPUT
.DIRECT
.RUN WAVE FUNCTIONS
**INTEGRAL
.DIPLEN
.DEROVL
.DERHAM
**WAVE FUNCTIONS
.CC
*CC INP
.CCSD
*DERIVATIVES
**END OF DALTON INPUT

Note that if several wavefunction models are specified, the gradient calculation is performed only for the ``lowest-level" model in the list.

For a geometry optimization:

**DALTON INPUT
.OPTIMIZE
**INTEGRAL
.DIPLEN
.DEROVL
.DERHAM
**WAVE FUNCTIONS
.CC
*CC INPUT
.CC(T)
**END OF DALTON INPUT