feat: adding `npm run server` task

This is work in progress.

`npm run server` starts a simple web server serving static assets in / and falling back to CouchDB API. /_utils works as well. Nothing is persisted, all data is stored in memory only.

I've removed the `npm run build` and `npm run watch` tasks, as they become obsolete with `npm run server` I'd say? 

For some reason browserify does not recompile when I change the src file, I've filed an issue:
https://github.com/andreypopp/connect-browserify/issues/10

fixes #8