Help button for many warning messages; Restored warning icon.

The error icon was gone because we are now using the ErrorDialog, which didn't have it.  So added back explicitly.  I decided to go with wxART_WARNING rather than wxART_ERROR because nearly all of these present as warnings.

src/WaveClip.cpp

@@ -1754,7 +1754,9 @@ void WaveClip::Resample(int rate, ProgressDialog *progress)
 
    if (error)
       throw SimpleMessageBoxException{
-         XO("Resampling failed.")
+         XO("Resampling failed."),
+         XO("Warning"),
+         "Error:_Resampling"
       };
    else
    {