Remove implicit creation of the Flocking environment

[colinbdclark]

At the moment, there are a number of places where the Flocking environment component will be implicitly created as a side effect of creating other components (such as a Synth). In practice, this behaviour leads to cases where an environment is unpredictably created too late in the process.

Instead, users should either manually create an environment, or use a new flock.composition component that takes care of this for them.

This will of course be an API-breaking change.