Add vision specific featurecoordinators

FeatureCoordinators for disparity, ocularity, spatial frequency and motion are added. This pull request depends on the related ImaGen pull request (https://github.com/ioam/imagen/pull/30). The motion feature coordinator needs time_dependent to be set to true.
If we really need this, it's fine, but I would otherwise prefer not to add any further new legacy code on top of legacy code.  I.e., can we not just use patterncoordinator directly from imagen?