Communications module: implement new broadcast object method

[Ellypse]

Some recent fixes made the sendObject method dynamically adapt to sending something to one person via whisper or broadcasting on a channel.

In favour of clarity and explicit usage, we instead want to add a broadcastObject method to the Communications module that will only handle broadcasting something on a specified channel.

Some code can be refactored and shared between this new function and the sendObject one. Existing usage of sendObject to broadcast data will have to be updated to use the new function.