Update config.yml

Allowed temporary switching of custom FNIRT inputs.
Update registration.py

Introduced switch to determine if FNIRT custom inputs apply or not (configurable in config.yml)
Merge branch 'development' of https://github.com/FCP-INDI/C-PAC into FCP-INDI-development

Conflicts:
	CPAC/registration/registration.py
	configs/config.yml