OPT: regiser_multimodal: added possibility to input init transformation (issue #1049)
OPT: regiser_multimodal: added possibility to input init transformation (issue #1049)

3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox