Replace launcher script with a symlink to the actual application

Now that we use --gapplication-service, launching the application
outside of DBus does the expected thing of opening a new window,
and the launcher becomes unnecessary.
The biggest advantage is restoring "jhbuild run gnome-weather"
from outside a jhbuild session, but we also get decent --help.
Application: only do the inactivity timeout when installed

The inactivity timeout is meant for the search provider. It's
not useful when testing the application itself.