Remove old motion model, use SmartSweeper instead of Translator

This pull request removes the legacy code for the old motion model (Sweeper) and changes the PatternGenerator for the new motion model from Translator to SmartSweeper in the direction2translation metaparameter function. The Translator and SmartSweeper calls are equivalent. This pull request depends on pull request https://github.com/ioam/imagen/pull/30 in ImaGen.