Advertise fast for at least 30 secs then slow down

On power up, advertise aggressively for at least 30 seconds then switch
to a longer interval to conserve battery life. This fast/slow pattern
is designed to balance connection response time and battery life.

When a disconnect event is received restart the fast/slow pattern.

When a failed connect event is received, restart the fast/slow pattern.

When the screen is activated and ble is not connected, restart the fast/slow pattern.

This pattern is consistent with Apple's BLE developer standards (QA 1931).

src/systemtask/SystemTask.cpp

@@ -233,6 +233,9 @@ void SystemTask::Work() {
           displayApp.PushMessage(Pinetime::Applications::Display::Messages::UpdateBatteryLevel);
           heartRateApp.PushMessage(Pinetime::Applications::HeartRateTask::Messages::WakeUp);
 
+          if (!bleController.IsConnected())
+            nimbleController.RestartFastAdv();
+
           isSleeping = false;
           isWakingUp = false;
           isDimmed = false;