Store deserialized data

I wonder how it took us so long without noticing.

We weren't storing the deserialized data, but the original posted data !
This preventing clean-up and defaulting values...

Specific case has to be handled manually for storing date/times into CouchDB. Best practice seems to serialize as ISO for ``Date.parse()`` to work natively. (source http://stackoverflow.com/a/4773320)

I propose this into master, since it is bug :) 

@natim, this may break daybed-pass since you are storing JSON as string. Luckyly, I had this check for a while in daybed-map https://github.com/leplatrem/daybed-map/blob/dev/models.js#L20-L22

This fixes #67