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.
Ok, no using the new Sweeper as the old Sweeper, then, in which case the new Sweeper should probably called Translator (if it works more like that one did). 

In any case, moving the old code into lissom.ty is fine, and will make nearly everything work, but won't work for snapshots.  And unfortunately, when I checked the list of tests, I saw that lissom.ty is indeed used there for snapshot tests, which will surely fail.  Obviously, we'll need to update those anyway, since lissom.ty is slated to disappear, but meanwhile it's good to keep them working as a safety check.  So, please try running the "exhaustive" tests, and possibly simply the "snapshot" tests, on your fork; they will presumably fail.  If so, maybe we should move Sweeper back, named e.g. OldSweeper for now, just to keep the tests running, and then delete it when we delete lissom.ty. 

I.e., the suggestion to move the old Sweeper to lissom.ty was mostly good, but because of this problem maybe it's not really a good idea. :-(