Prioritize and display -testsafemode status in UI

Like in a real world situation, a safe mode test should also be visible in the
UI. A test of safe mode is furthermore mostly relevant for developers, so it
should not be overwritten by a warning about a pre-release test build.
Merge pull request #5356

7357893 Prioritize and display -testsafemode status in UI (dexX7)
Merge remote-tracking branch 'bitcoin/master'