app: Load plugins early

Fixes: 574e1f79 ("application: Drop ignore_activation flag") Closes: #718 (closed)

Thanks @Arnavion for the detailed report.

@devrtz I went for the minimal fix here, we should get rid of all the start_proper invocations. We could preserve the set-plugin-names option by moving it to local-options in case it is needed (e.g. to hardcode ofono?)