Time for some upvotes

Yesterday evening I did some work on setting up an initial upvote system. Initially this will be very simple:

plan -> upvote <- user

These are stored in the Postgres database but we can move this to other more efficient storage systems later on if needed. So as long as you log in, you can upvote a plan. Having many upvotes does nothing at the moment, so there is no weight attached to it when displaying plans on the home timeline or something. It's still based on newest creation date for now.

This will be changed too: when not logged in, it will show the latest plans. But when logged in, it will show the latest plans from friends (after I implemented this).