web app initialized twice(?)

Upon start, the webapp prints its own initialization message twice, e.g.:

timira ➜  swh-web-ui git:(master) bin/swh-web-ui
SWH Web UI available at http://127.0.0.1:6543/
debug: True
SWH Web UI available at http://127.0.0.1:6543/
debug: True

That's weird. Is the app being initialized twice? Also, why are we printing ourselves the app location, given Flask knows how to do that itself (when running in debug mode, at least)?

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Migrated from T165 (view on Phabricator)