Move Trebuchet to default.xml

Even though this is a "custom" app, it is still a core part of android
that needs to be up to date with security patches and QPR updates.
Move it to the main manifest to make aosp-merger work without
hardcoding Trebuchet in the merge scripts.

Change-Id: I1031d90067f4e3f87c93f90f527271c9ad578225
diff --git a/default.xml b/default.xml
index 500ec97..77ab751 100644
--- a/default.xml
+++ b/default.xml
@@ -905,6 +905,7 @@
   <project path="packages/apps/TimeZoneUpdater" name="platform/packages/apps/TimeZoneUpdater" groups="pdk" remote="aosp" />
   <project path="packages/apps/ThemePicker" name="LineageOS/android_packages_apps_ThemePicker" groups="pdk-fs" />
   <project path="packages/apps/Traceur" name="platform/packages/apps/Traceur" groups="pdk-fs" remote="aosp" />
+  <project path="packages/apps/Trebuchet" name="LineageOS/android_packages_apps_Trebuchet" groups="pdk-fs" />
   <project path="packages/apps/TvSettings" name="LineageOS/android_packages_apps_TvSettings" groups="pdk-fs" />
   <project path="packages/apps/TV" name="platform/packages/apps/TV" groups="pdk" remote="aosp" />
   <project path="packages/apps/UniversalMediaPlayer" name="platform/packages/apps/UniversalMediaPlayer" remote="aosp" />