added lumpedVolumeDeclarations

removed TOpStart
propagated mixing volume properties
set connections to mixing volume such that flow 'noFlowReversal' is possible

@rubenbaetens the parameter TOpStart is removed. T_start is added but only applies to the mixing volume so sum.y(start) is no longer set. Is this a problem for you? In the end the result should be the same I think.