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/guitar2.yml

@@ -0,0 +1,34 @@
+name: Guitar2
+numvoices: 1
+units:
+    - type: envelope
+      id: 1
+      parameters: {attack: 0, decay: 0, gain: 128, release: 72, stereo: 0, sustain: 128}
+    - type: envelope
+      id: 2
+      parameters: {attack: 0, decay: 58, gain: 128, release: 0, stereo: 0, sustain: 0}
+    - type: noise
+      id: 3
+      parameters: {gain: 128, shape: 127, stereo: 0}
+    - type: mulp
+      id: 4
+      parameters: {stereo: 0}
+    - type: filter
+      id: 5
+      parameters: {bandpass: 1, frequency: 32, highpass: 1, lowpass: 1, negbandpass: 0, neghighpass: 0, resonance: 128, stereo: 0}
+    - type: delay
+      id: 6
+      parameters: {damp: 16, dry: 128, feedback: 128, notetracking: 1, pregain: 128, stereo: 0}
+      varargs: [10787]
+    - type: filter
+      id: 84
+      parameters: {bandpass: 1, frequency: 24, highpass: 1, lowpass: 1, negbandpass: 0, neghighpass: 0, resonance: 128, stereo: 0}
+    - type: mulp
+      id: 85
+      parameters: {stereo: 0}
+    - type: pan
+      id: 86
+      parameters: {panning: 64, stereo: 0}
+    - type: outaux
+      id: 10
+      parameters: {auxgain: 24, outgain: 64, stereo: 1}