Creates core app.
Creates TimestampedModel in core/models.py
Makes Dog a subclass of timestamped model and sets up dog_photo_upload_to method.
Creates thumbnailing methods and template tag in core app.
Updates dog_list template to use thumbnail template tag and rounds out markup.
Adds MAXIMUM_THUMBNAIL_SIZE to settings.
Adds MEDIA_URL url to whosyourdoggy/urls.py