Refactor Termination Criterion regarding Iterations Number

[dinkelbachjan]

As discussed in PR #213, the iterative solution procedure, which currently allows for the performance of corrector steps by PCM and TPM synchronous generator models, needs a refactoring with respect to the implementation of its termination criterion regarding the maximum number of allowed iterations. Instead of checking in each of the synchronous generator components individually whether the number of the component iterations has reached the specified maximum allowed number, this should be checked "globally" instead by the MNASolver. The MNASolver can count the number of performed iterations and compare it with the predefined allowed maximum. We currently do not expect that component-specific maximum values are of interest. This can be implemented by using the already available mIter. Additionally, this requires a mechanism that allows for adding the MNASolver member variable to the data logger.