Creating Masses from any tensors, and Proportions from any Masses

- resolves issue #181
- Masses can be created from any Tensor, there are even implicits in the MassesVariable object
- Proportions can be created from any Masses object via MassesProportions, (argument is either a Masses object or a Tensor)
- some minor cleaning
- additional Tensor based on a HashMap which is also growable