Revert "Move DrakeFunctionConstraint to drakeFunction.Constraint"

This reverts commit b368e4b3ec15a4d5574b53407c92f184b47fbdcd.
Move drakeFunction package to solvers

Revert adding drake root in addpath_drake
This reverts commit c4ad674b054edeae696e82605968c9ddf3cd07a4.