application-mode: improve detection of redirects to uris that are part of the app

The heuristics that was being used caused problems with logging in to some applications,
such as using Phabricator to authenticate to Mattermost. With the availability of tabs
for application mode the heuristic is less critical, but it still pays off to provide a
good experience to the user by keeping the application-related uris in the same tab.

https://bugzilla.gnome.org/show_bug.cgi?id=788845