Move call to optimizers in mode-computing to separate file to allow othe...

...r function to access all integrated optimizers

- also moves several options to subfields of options structure
- allows setting options of newrat
- requires newrat to have compatible kalman_algo specified in order for it to not change options_
- explicitly disallows using analytical derivation with numerical gradient (before the numerical gradient request was overwritten)
- always outputs hessian returned by optimizer (empty matrix if not computed) and deletes subsequent overwriting if cova_compute=0