message: Improve staking indicator
  'Not staking, staking is disabled' was never shown
  'Initializing staking...' is now shown instead 'Not staking because you don't have mature coins' during staker thread initialization
diff: @@ -288,15 +288,15 @@ void SpectreGUI::pageLoaded(bool ok)
  bridge->populateAddressTable();
  initMessage(splashScreen, ".Start UI.");
  - walletModel->checkBalanceChanged(true);
  - if (GetBoolArg("-staking", true))
  {
  + LOCK2(cs_main, pwalletMain->cs_wallet);
  + walletModel->checkBalanceChanged(true);
  updateStakingIcon();
  - if (!initialized)
  + if (GetBoolArg("-staking", true) && !initialized)
  {
  QTimer *timerStakingIcon = new QTimer(this);
  connect(timerStakingIcon, SIGNAL(timeout()), this, SLOT(updateStakingIcon()));
  - timerStakingIcon->start(15 * 1000);
  + timerStakingIcon->start(5 * 1000);
  }
  }
  @@ -1131,6 +1131,7 @@ void SpectreGUI::updateStakingIcon()
  (pwalletMain && pwalletMain->IsLocked()) ? tr("Not staking because wallet is locked") : \
  (vNodes.empty()) ? tr("Not staking because wallet is offline") : \
  (clientModel->inInitialBlockDownload()) ? tr("Not staking because wallet is syncing") : \
  + (!fIsStaking) ? tr("Initializing staking...") : \
  (!nWeight) ? tr("Not staking because you don't have mature coins") : \
  tr("Not staking"));
  }
  