For events, use a slug in the URL instead of the event ID

Use MongoDB to store slug information

[JOINDIN-250] [JOINDIN-256]
Merge previous commit
storing event uri in the db, using it to fetch event data later on
fetching the event object and sending an array of data to the template
adding the page_header block to the layout template (in the wrong place, probably)
Merge pull request #17 from lornajane/routing-and-data

Routing and database ideas