allow for multi-echo reconstruction for MGRE
allow for multi-echo reconstruction for MGRE

- basically multi-echo parallel imaging using NLINV

sidward/bart,mrirecon/bart,sidward/bart,sdimoudi/bart,sidward/bart,sdimoudi/bart,mrirecon/bart,mrirecon/bart,sdimoudi/bart,sdimoudi/bart,sdimoudi/bart,sidward/bart,mrirecon/bart,mrirecon/bart,sidward/bart