Code refactoring for model.cpp

The model.ccp file contains 1500+ lines of code. To improve readability and the code structure we should refactor the code and separate the following functions:

• FBS functions: model_fbs.cpp already there
• Config functions: model_config.cpp anything for reading files and parameters = anything that happens in constructor + reading profiles (should happen in constructor as well...)
• Init functions for networks: model_init_networks.cpp anything called in Model::init() that creates and initializes el. or communication networks
• Init functions for agents: model_init_agents.cpp anythin called in ``Model::init()` that created and initializes agents and their behaviors