Separate pure and side-effecting code

[samertm]

To make it easier to use sw-toolbox as a library, this PR moves all the helper and listener functions out of sw-toolbox.js so they can be imported without setting up the event listeners.

Tests in Chrome 51 pass locally.

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[samertm]

I signed it!

[googlebot]

CLAs look good, thanks!

[addyosmani]

This cleans up the main sw-toolbox entry quite a bit while making it easier to just pull in the helpers. It's also passing our current CI tests. I'm personally fine with this change, but let's see what @jeffposnick and @gauntface think.

[wibblymat]

A wild @wibblymat appears!

I agree that this change makes sense for people who want to use the helpers on their own.

[jeffposnick]

👍 from my perspective as well.

As an FYI, we're thinking about similar topics in GoogleChrome/workbox#44

I see this PR a move in that direction using the current codebase, which should be continue to be relevant for a while yet. But if you have any feedback about the proposals tracked in that issue, that would end up being the most meaningful longer term.

[samertm]

Thanks! I'll take a look at that issue.

[samertm]

Friendly ping to merge this in. :)