moved visual waveforms to block

This should be nicer, however it has a bug that I need to fix

app/audio/audiovisualwaveform.cpp

@@ -233,6 +233,29 @@ void AudioVisualWaveform::Shift(const rational &from, const rational &to)
   length_ += (to-from);
 }
 
+void AudioVisualWaveform::TrimIn(const rational &length)
+{
+  for (auto it=mipmapped_data_.begin(); it!=mipmapped_data_.end(); it++) {
+    rational rate = it->first;
+    double rate_dbl = rate.toDouble();
+    Sample& data = it->second;
+
+    int chop_length = time_to_samples(length, rate_dbl);
+
+    if (chop_length == 0) {
+      continue;
+    }
+
+    if (chop_length > 0) {
+      data = data.mid(chop_length);
+    } else {
+      data.insert(0, -chop_length, SamplePerChannel());
+    }
+  }
+
+  length_ -= length;
+}
+
 AudioVisualWaveform::Sample AudioVisualWaveform::GetSummaryFromTime(const rational &start, const rational &length) const
 {
   // Find mipmap that requires