Projection.weight and Projection.exponent are never applied

[jvesely]

All projections expose weight and exponent parameters.
Although there is code processing the parameters, the values are never used during computation.

Simple testing using MappingProjection gives the same result for all configurations below:
MappingProjection(sender=..., receiver=...)
MappingProjection(sender=..., receiver=..., exponent=5)
MappingProjection(sender=..., receiver=..., weight=-5)
MappingProjection(sender=..., receiver=..., exponent=5, weight=-5)