Add ALT Routing

[paulheinr]

To bring back routing to this project, the ALT Algorithm should be implemented.

Router:

• Implement ALT routing
• Implement ALT landmark selection
• Implement tests
• Implement queue (Use BinaryHeap and update via remove and add)

Router updating:

• Implement generic trait for TravelTimesMessageBroker
• Implement specific non MPI MessageBroker

Adapting plans:

• Add layer between router and simulation -> plan modificator, which takes a mutable reference to an agent and modifies its next leg

General changes:

• Use IntMap instead of HashMap or BTreeMap