Add CC-BY sounds, bringing fgdata c172p up to date.

Now matches e0a32e62d9390f796feac6f5e1818323f970bbf5
completely.

Aircraft/c172p/Thanks

@@ -0,0 +1,3 @@
+- Stall sound source: from a Youtube video entitled "Stalling and spinning with a Cessna 152" by Morsule. Link: https://www.youtube.com/watch?v=zTq8Jvoks2U
+- Parking brake sound source: from a sound file entitled "Old Lever Pull" by DrMinky. Link: http://freesound.org/people/DrMinky/sounds/167048/
+- Trim wheel sound source: from a sound file entitled "rubber.wav" by datasoundsample. Link: http://freesound.org/people/datasoundsample/sounds/41631/

Aircraft/c172p/c172-sound.xml

@@ -243,7 +243,7 @@
   <stall>
    <name>stall</name>
    <mode>looped</mode>
-   <path>Sounds/stall.wav</path>
+   <path>Sounds/stall2.wav</path>
    <condition>
     <and>
      <property>sim/alarms/stall-warning</property>
@@ -360,7 +360,7 @@
     <switch>
         <name>click-parking-brake</name>
         <mode>once</mode>
-        <path>Sounds/click.wav</path>
+        <path>Sounds/lever.wav</path>
         <condition>
             <property>/sim/model/c172p/sound/click-parking</property>
         </condition>
@@ -844,7 +844,7 @@
     <dial>
         <name>dial-trim-wheel</name>
         <mode>in-transit</mode>
-        <path>Sounds/scroll.wav</path>
+        <path>Sounds/trim.wav</path>
         <property>/controls/flight/elevator-trim</property>
         <position>
             <x>-0.3660</x>