Update 2D and 3D geometry to support multi-domains

.gitignore

library/MultiRegions/DisContField.cpp

library/MultiRegions/ExpList.cpp

library/SpatialDomains/Geometry.cpp

library/SpatialDomains/Geometry.h

library/SpatialDomains/Geometry1D.cpp

library/SpatialDomains/Geometry1D.h

library/SpatialDomains/Geometry2D.cpp

library/SpatialDomains/Geometry2D.h

library/SpatialDomains/Geometry3D.cpp

library/SpatialDomains/Geometry3D.h

library/SpatialDomains/SegGeom.cpp

library/SpatialDomains/SegGeom.h