Picture upload links might be issued from the server but not used by the client

[abrahamq]

Right now, the client asks the server for a signed url, the server (which has credentials)
asks s3 for a signed url where the client can PUT an image. There's a corner case where the
server asks for a signed url, but the client doesn't actually PUT the image (connection drops, user backs out, so on.)

Here's a fix: use the lambda code to touch our database after it does the compression so that it tells us that an image url is present.