Replace fe_multi_stream_test with fe_simulated_streams, a rewrite in Go

Replace the C++ simulated stream generator with a Go based one. The motivation was to add a richer control interface to the application in order to allow adding/removing/adjusting the simulated models on the fly during tests. This is done by adding a http admin interface that allows via http requests to query the status of the simulation and modify it.

Go was used to implement this rather than C++ as the volume of code or supporting libraries that would be needed was smaller.