Update bell

- Don't add the bell to the archive to keep it small a simplify
  licensing. Also bells seem to be rarely used with terminal emulators.
- Don't play the bell directly from the Terminal node by adding an
  AudioStreamPlayer, but make it easy to tune the "bell" signal behavior
  from the Terminal node so that only an AudioStreamPlayer node's play()
  method needs to be connected to it.
- Keep the bell.wav sound around for testing/demo.

themes/audio/bell.wav.import

@@ -0,0 +1,21 @@
+[remap]
+
+importer="wav"
+type="AudioStreamSample"
+path="res://.import/bell.wav-0bb68f27c3e29a9aad676dc03d89b163.sample"
+
+[deps]
+
+source_file="res://themes/audio/bell.wav"
+dest_files=[ "res://.import/bell.wav-0bb68f27c3e29a9aad676dc03d89b163.sample" ]
+
+[params]
+
+force/8_bit=false
+force/mono=false
+force/max_rate=false
+force/max_rate_hz=44100
+edit/trim=false
+edit/normalize=false
+edit/loop=false
+compress/mode=0