Implement unit test for ParameterSet class

This feature implements unit tests for parameter set class checking internal consistency, copy/assignment/swap operation, comparison operators and residual calculation. Further tests for checking the correction of parameter values if they are out-of-bounds (e.g. for periodic variables like angles) are also included.

Fix a problem in the assignment operator of the ParameterSet class. The signature of a copy-assignment operator and a move-assignment operator are ambiguous. The copy-assignment operator is replaced by a non-copy const-reference assignment operator.

The documentation is extended to include links to the relevant unit tests.