WIP: Lively store

Serialization interface that provides very simple access (key/value read and writes) to different backends. Supposed to be used for per-app persistence. Possibly also an option for storing worlds and for a future wiki.

Supported backends right now:

- JS object
- files
- CouchDB (needs [couchdb subserver](https://github.com/LivelyKernel/subserver-couchdb.git))