Auto-load particle and sound files when loading from bbmodel

Closes #1309

css/panels.css

@@ -1383,6 +1383,9 @@
 		stroke-width: 0;
 		pointer-events: initial;
 	}
+	.keyframe .keyframe_waveform > polygon:hover {
+		fill: var(--color-accent);
+	}
 
 	#timeline_graph_editor {
 		position: absolute;

js/animations/keyframe.js

@@ -9,9 +9,23 @@ class KeyframeDataPoint {
 		if (data.values) {
 			Object.assign(data, data.values)
 		}
+		let file_value_before = this.file;
 		for (var key in KeyframeDataPoint.properties) {
 			KeyframeDataPoint.properties[key].merge(this, data)
 		}
+		if (isApp && data.file && !file_value_before) {
+			if (this.keyframe.channel == 'sound' && !Timeline.waveforms[this.file]) {
+				Timeline.visualizeAudioFile(this.file);
+			} else if (this.keyframe.channel == 'particle') {
+				try {
+					Blockbench.read([this.file], {}, (files) => {
+						Animator.loadParticleEmitter(this.file, files[0].content);
+					})
+				} catch (err) {
+					console.log('Could not load particle effect for', this.file)
+				}
+			}
+		}
 	}
 	getUndoCopy() {
 		var copy = {}

js/util/property.js

@@ -71,7 +71,7 @@ class Property {
 		if (typeof this.default == 'function') {
 			return this.default(instance);
 		} else if (this.isArray) {
-			return this.default.slice();
+			return this.default ? this.default.slice() : [];
 		} else if (this.isObject) {
 			return Object.keys(this.default).length ? JSON.parse(JSON.stringify(this.default)) : {};
 		} else {