Python 3 support + additional applications

• SimpleReg for Python 2 and 3
• New applications include
  • simplereg_register_landmarks: Rigid registration of two point sets using the Coherent Point Drift (CPD) algorithm
  • simplereg_transform: Transformation between FSL/NiftyReg/(Simple)ITK Transform objects; landmark to label handling
  • simplereg_resample: resampling script; In addition to standard interpolators, Oriented Gaussian Interpolation is available too (requires ITK_NiftyMIC currently)