Start integration of the builder lib in the gradle plug-in

First step: move to the BuildType and ProductFlavor classes
from the builder library.

Change-Id: Ib83c590ff7dbf38774022d7539634835de9f31c0
diff --git a/settings.gradle b/settings.gradle
index b9845fa..1928fe1 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -1 +1,2 @@
+include 'builder'
 include 'gradle'