curve manager changes

-changed _get_oc_model_settings to _get_oc_model_settings_copy so that
clients don't need to ensure they're working on a copy of current
settings

- fixed bug in _get_instrument_sensitivity_to_input_change_dict method
where permutations to sandbox curve where being done with the
_set_model_settings method in stead of the _set_server_settings method.
this caused settings for sandbox_month to cache instead of actual month
settings