Updated Models and Fixed ProductSerializer

I found a way to auto add created_at and updated_at, so I did that.
Also fixed some syntactical errors with the ProductSerializer.

Adding a product now works as expected, although we are returning
vendor *id* rather than the entire serialized vendor object. I believe
this is trivial, as the client should already have this data after
authentication is complete.

The RWDProductView view remains untested.