OGM-400

* `byte`s and `long`s are stored as JSON numbers
* `Calendar`s are stored as ISO8601 strings, including TZ information
* `Date`s are stored as ISO8601 strings, in UTC, without TZ information

Note there is no standardized date format in JSON and thus CouchDB. After some research, using ISO8601 Strings seems as the most commonly used approach to me.