Issue 158

This branch solves several bugs related to the source manager:

1. The shared state of the building between the main thread and the source thread may not be synchronous. Therefore, duplicate agents can be generated (having the same position).
2. The main thread spawns the source thread. However, depending on the OS-scheduler the second thread may be lagging and does not start immediately.

Both problems are solved. Documentation is within issue #158 (closed)