Assyncronous thread listing and updating.

Application is now asynchronous and runs with Gevent. Taking advantage
of that, it uses Server-Sent-Events to implement a stream of Thread
modification/creation to avoid data pooling entirely. Also pushed a few
enhancements and fixes:

    * Normalizing CSS coding style.
    * Created TimeStampedModel, since having a Model with creation and
      modification timestamps is a common pattern.
    * Fixed a bug on db.py, where DateTimeField weren't validating
      correctly.