Bug fixes for motion corrected sequence class
Refactoring of 2D HMM and work on 3D HMM.

Tests pass.
Working 3D HMM, though still contains rough hacks.

2D tests still pass. 3D displacements reasonable.
trim_coords for 3D displacements
Fixed exporting of frames.
Merge pull request #52 from pkaifosh/3D-HMM