Handle startup errors better
If there's an unrecoverable error early in startup (
Application.Client.startup or in
Application.Controller's ctor) at the moment we don't handle it very well, commonly by crashing.
Problems that cause this include invalid config dirs (#1028 (closed)) or failures when init'ing required services (libsecret, gcr/gck, folks, etc).
It would be good to show an error dialog rather than straight up crashing, maybe with a pointer to the FAQ entry about required services if it looks like one is missing, and a problem report dialog so we can collect info for bug reports.