Issue30 system block

This replaces https://github.com/iea-annex60/modelica-annex60/pull/101 which is against the master instead of the development branch.

@Mathadon made the following changes:
removed system blocks
set default parameter values
added PartialTwoPort and PartialTwoPortTransport

I merge this in the development branch to allow testing and possible revisions before it is merged to the master.