SignalGenerator: Port name and icons changes

signal_generator/application.fam

@@ -1,6 +1,6 @@
 App(
     appid="signal_generator",
-    name="Signal Generator",
+    name="[GPIO] Signal Generator",
     apptype=FlipperAppType.EXTERNAL,
     entry_point="signal_gen_app",
     requires=["gui"],

signal_generator/views/signal_gen_pwm.c

@@ -3,6 +3,8 @@
 #include <gui/elements.h>
 #include <signal_generator_icons.h>
 
+#include <assets_icons.h>
+
 typedef enum {
     LineIndexChannel,
     LineIndexFrequency,