indexed-db doc from 192d5a3642
Freeze object, style correction, prefix url correction

* all strings changed to double quotes
* freeze `exports.indexedDB`
  - (heritage.extend, rather than `object.Create`)
  - includes test
* use `addon://` fake scheme in principal
* makeFunc replaced with `bind`
* sanitized "indexeddb" uri for principal
indexedDB docs reflect openForPrinciple

Doc updates:

* external example usage
* changed 'aside' to reflect current bug status on protocols, principle
* removed outdated notes on Database Naming