Clean up bus initialization

[dnarvaez]

• We now explicitly initialize the bus in activity, or in beforeEach for tests. This is more predictable that initializing whenever the bus module is loaded. Also it will allow to write tests that uses a mock implementation of the bus socket.
• Environment setup is factored out to its own module. It will allow other modules which needs to get values from the environment to do so.
• The environment is taken from a single window.sugar.environment object.