cleanup: more Coverity silencing

Mostly irrelevant std::move() stuff of copy-on-write Qt objects,
a few real bugs, a timestamp_t downconversion and some codingsyle
adaptation.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

stats/statsaxis.cpp

@@ -279,7 +279,7 @@ void ValueAxis::updateLabels()
 {
 	QLocale loc;
 	auto [minString, maxString] = getFirstLastLabel();
-	int numTicks = guessNumTicks({ minString, maxString});
+	int numTicks = guessNumTicks({ std::move(minString), std::move(maxString)});
 
 	// Use full decimal increments
 	double height = max - min;