Compute cord/CSF ratio and removing T1w bloc (#64)

Fixes Consider quantifying the ratio cord/CSF signal #63

* Removed T1w block

* Put back vertebral labeling on the T2starw scan

* Cosmetic changes

* Removed temp fix

* Create CSF mask

* Extract signal in T2starw scan in SC and CSF

* Display curves (WIP)

* Create curves (only for CoV and CP)

* Updated intro