Switch from deprecated static-favicon to serve-favicon

Closes #275. Will require update to [`generator`](https://github.com/krakenjs/generator-kraken/) to re-enable and configure correct favicon.

I'm not sure I love this fix, but for the short-term it should work. It entails:
- Update dependency to `serve-favicon`
- Disable favicon middleware by default.
- Configure favicon middleware to use icon provided by `kraken-js`, allowing applications to start. Unless enabled, this favicon will not be used out of the box.