ENH: Level-set domains different from image domain

Added m_DomainOffset to store offset to each levelset (uses offset to evolve
N-level-sets)

Changed variable names to match ITK conventions

Change-Id: Icaae5e7a3df946e5159ca2dd3d8229ef8ed6c478
Merge topic 'LevelSetsv4DomainPartition'

8662120 ENH: Level-set domains different from image domain