Release the generated service worker to the public domain

[marco-c]

#38 was about the template files, but I think we should also release the generated service worker to the public domain in order to let the developers choose their own license.

We can either do this by removing the sw-precache dependency and rolling our own service worker or by using the templateFilePath option [1] of sw-precache using our own service worker template.

[1] https://github.com/GoogleChrome/sw-precache#templatefilepath-string

I think @delapuente was looking into this, right?

[mykmelez]

Yes, @delapuente is looking into this!

[mykmelez]

@delapuente fixed this in #188!