Add config variables to initialize service worker

[pmitros]

@JohnDamilola Would it be possible to please break this up into two pull requests, one with functionality changes, and one with formatting? It's very hard to see what changed if it's all in one commit.

[pmitros]

@JohnDamilola Brad and I reviewed this PR. Collin and I had misunderstood what was going on. Please disregard above comment and accept my apologies. As high-level feedback on this PR:

• A lot more stuff goes into the wrapper function than we should have.
• In particular, the logging code is cut-and-paste into this, but we will use it other places. Putting it inside will make it harder to tease out later. We'd like to be able to cleanly abstract this out.
• The initialization is needed in order to send events to the server, but not to receive them into our queue. We want to make sure this works from the time the browser is opened. The reason we had a the complexity of an FSM in the code was to make sure we could receive events from tabs while the extension was initializing. We don't want to lose events while the browser + extension are loading. This code: loadConfig().then((config) => {main(config);}) leads to a race condition where we cannot receive events until we've loaded the config. That means we might drop events if we open up a new browser window pointed at Google Docs depending on order of events.