Add fish silhouettes to Logbook

ui/logbook_silhouette.gdshader

@@ -0,0 +1,8 @@
+shader_type canvas_item;
+
+uniform vec4 silhouette_color : source_color = vec4(0.22, 0.23, 0.24, 1.0);
+
+void fragment() {
+	vec4 source = texture(TEXTURE, UV);
+	COLOR = vec4(silhouette_color.rgb, source.a * silhouette_color.a);
+}