Fix IDEUI-221 Better app health check

Various enhancement on the app health check that was partly bugged:
* when the application URL is displayed after 30' if app health check
can't determine if app is available, now a notification popup message
is displayed and app panel is updated,
* if app health check succeeds, this fallback 30' timer is cancelled,
* app failure now triggers on necessary cleaning on the console.
Merge pull request #233 from stephanedaviet/IDEUI-221

Fix IDEUI-221 Better app health check