Refresh forums more often.

Refreshing on appear now also happens when there are no forums, and when there
are any forums that were created as part of parsing posts.
Push built-in browser, don't show modally.

Nicer flow in my eyes.
Give built-in browser a default title.
Push user profile, instead of modal, on iPhone.

Feels nicer.
Fix saving parsed user profiles.

By not setting the user ID we were creating then updating a User instance with
a nil user ID. This appeared in the interface when viewing a profile that had
e.g. an AIM username, then viewing a profile that did not. The first user's AIM
username would erroneously appear under the second user.
Clear unset user profile entires when saving.

If someone deletes their e.g. AIM username, we should too.