End of orientation zero group experiment

End of orientation zero group experiment

Adds an experiment that codes an end-of-orientation symbol
for every eligible zero encountered in scan order.

This cleans out various other sub-experiments that were part
of the origiinal patch, which will be later included if found
useful.

Results are slightly positive on all sets (0.1 - 0.2% range).

Change-Id: I57765c605fefc7fb9d1b57f1b356843602abefaf