feat(tracker): add menu to load instrument presets

The presets are embedded in the executable, so there's no additional files.

Closes #91

tracker/presets/rhodes.yml

@@ -0,0 +1,27 @@
+name: Rhodes
+numvoices: 1
+units:
+    - type: envelope
+      id: 1
+      parameters: {attack: 0, decay: 96, gain: 128, release: 64, stereo: 0, sustain: 0}
+    - type: oscillator
+      id: 2
+      parameters: {color: 128, detune: 73, gain: 128, lfo: 0, phase: 0, shape: 64, stereo: 0, transpose: 64, type: 0}
+    - type: send
+      id: 3
+      parameters: {amount: 96, port: 2, sendpop: 1, target: 5}
+    - type: oscillator
+      id: 5
+      parameters: {color: 128, detune: 64, gain: 128, lfo: 0, phase: 64, shape: 64, stereo: 0, transpose: 64, type: 0}
+    - type: mulp
+      id: 6
+      parameters: {stereo: 0}
+    - type: filter
+      id: 175
+      parameters: {bandpass: 0, frequency: 48, highpass: 0, lowpass: 1, negbandpass: 0, neghighpass: 0, resonance: 64, stereo: 0}
+    - type: pan
+      id: 176
+      parameters: {panning: 64, stereo: 0}
+    - type: outaux
+      id: 177
+      parameters: {auxgain: 4, outgain: 96, stereo: 1}