Unify sleepy code to std::thread sleep

src/AppFrame.cpp

@@ -783,11 +783,7 @@ void AppFrame::OnIdle(wxIdleEvent& event) {
     demodWaterfallCanvas->processInputQueue();
   
     if (!this->IsActive()) {
-#ifndef _WIN32
-        usleep(25000);
-#else
-        Sleep(25);
-#endif
+        std::this_thread::sleep_for(std::chrono::milliseconds(25));
     }
 
     event.RequestMore();

src/process/FFTVisualDataThread.cpp

@@ -36,11 +36,7 @@ void FFTVisualDataThread::run() {
     
     while(!terminated) {
         
-#ifndef _WIN32
-        usleep(15000);
-#else
-        Sleep(15);
-#endif
+        std::this_thread::sleep_for(std::chrono::milliseconds(15));
         
         int fftSize = wproc.getDesiredInputSize();