Fix refresh check and improve test menu (EXPOSUREAPP-4049) (#1772)

* Remove "lastTimeDiagnosisKeysFromServerFetch" and replace it with less missleading data.
While it was called "lastTimeDiagnosisKeysFromServerFetch" it was actually "last time we submitted keys to google".

* To decide whether to refresh in "onResume", we now use "has there been any submission to the ENF?"
* To display a timestamp on the risk card, we take the last successful submission to the ENF as the risk card displays the calculation results based on the latest submission. While we could use the last calculated risk level result timestamp, we currently also trigger risk calculations if there are no new submissions to the ENF, which would mean the timestamp is updated even though the result is not based on new data.

I've also fixed the test fragment button behavior and added descriptions, the "Reset risk level" button surfaced the initial issue because it behaved like a "do a 75% data reset" button.

* Tests and LINTs

Co-authored-by: harambasicluka <64483219+harambasicluka@users.noreply.github.com>
Co-authored-by: Ralf Gehrer <ralfgehrer@users.noreply.github.com>