NEW: added new script to compute and display Ernst angle
NEW: added new script to compute and display Ernst angle

Former-commit-id: 3a7246f99fd2d0ec14f24d0034776899aae2f33d
Former-commit-id: 1242cd72f5f1e58dff8a4192201a0202991031d4
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox