Rename GesturePreviewTrail.java -> GestureTrail.java

Try reducing some confusions between GesturePreviewTrail.java and GestureTrailsPreview.java

Change-Id: I5fe2ee740cf1b32210530188153f6f6937e34b68
diff --git a/java/res/values/config.xml b/java/res/values/config.xml
index 23b5794..742860b 100644
--- a/java/res/values/config.xml
+++ b/java/res/values/config.xml
@@ -75,9 +75,9 @@
     <bool name="config_show_more_keys_keyboard_at_touched_point">false</bool>
     <bool name="config_block_potentially_offensive">true</bool>
     <integer name="config_gesture_floating_preview_text_linger_timeout">200</integer>
-    <integer name="config_gesture_preview_trail_fadeout_start_delay">100</integer>
-    <integer name="config_gesture_preview_trail_fadeout_duration">800</integer>
-    <integer name="config_gesture_preview_trail_update_interval">20</integer>
+    <integer name="config_gesture_trail_fadeout_start_delay">100</integer>
+    <integer name="config_gesture_trail_fadeout_duration">800</integer>
+    <integer name="config_gesture_trail_update_interval">20</integer>
     <!-- Static threshold for gesture after fast typing (msec) -->
     <integer name="config_gesture_static_time_threshold_after_fast_typing">500</integer>
     <!-- Static threshold for starting gesture detection (keyWidth%/sec) -->