Include note name in estimated pitch label.

e.g. it might show "440Hz (A4)"
This should fulfill tlecomte#234

friture/spectrumPlotWidget.py

@@ -137,6 +137,18 @@ def set_baseline_displayUnits(self, baseline):
     def set_baseline_dataUnits(self, baseline):
         self._baseline = Baseline.DATA_ZERO
 
+
+
+    def freq_to_note(freq: float) -> str:
+        # number of semitones from C4
+        # A4 = 440Hz and is 9 semitones above C4
+        semitone = round(np.log2(freq/440) * 12) + 9
+        # now, from C4
+        semitone += 9
+        octave = int(np.floor(semitone / 12)) + 4
+        notes = ["C", "C#", "D", "D#", "E", "F", "F#", "G", "G#", "A", "A#", "B"]
+        return f'{notes[semitone % 12]}{octave}'
+
     def setdata(self, x, y, fmax, fpitch):
         if not self.paused:
             if fmax < 2e2: