Implement the transfroms and mapping steps in separate functions.
Update testFourierTransform and timers.

Functions performing the various mappings and transposes are moved
to BasisMapping.

The name switch makes the function names consistent with fwd and bwd
transforms in FourierTransform

The change of sign makes the value of the force consistent with
the definition of the force ( -grad(E) )
A positive value of the constraint force tends to increase the
constraint value.
The change of sign of PairForce makes it such that a positive
PairForce value tends to increase the bond length.
The value of the PairForce needed to compensate for a distance
constraint is opposite to the force acting on the constraint.