Logged-in users visiting TruSat.org should see the Catalog first

[mikeville]

If a user has registered an account to submit satellite observations, they shouldn't have to see the TruSat landing page every time they visit TruSat.org. This landing page was designed for people who don't yet have accounts.

Instead, let's redirect logged-in users to https://trusat.org/catalog/priorities, which should be more useful to returning registered users.

A side-effect of this is that logged-in users won't be able to see the logged-out landing page until they log out, so we'll need to make sure that any essential info on the landing page can be easily found elsewhere in the docs.