Feature request: Improve speed of planet updates

[dtiburon]

Currently there's a cron job that updates the planets that updates every 15 mins or so. It would be nice if it could selectively update when a feed is added/changed so there's no wait after a change is made.

[jvasile]

In particular, when you make a new planet and add feeds to it, you can't immediately look at it. This is a problem for new users who get the prompt to set up their planets when they try to visit the planet they just set up.