Separated network restrictions from the main model module. Tests work. Started to work on converters and prices but did not test.

Limitations to the number of incoming and outgoing directed arcs are now equivalent. Revised the way to declare network objects.

Revised classes for investments in generic arcs and in district heating trenches. Updated converter and dynsys tests.

Revised ResourcePrice class and methods. Added tests for problem simplification routines. Started problem identification method.