Downgrade to java 1.6

This CL removes java 1.7 code so that we can easily integrate
w/ Idea.

It also partially removes dependency on ModelAnalyzer for
interface generation so that we can call it from the Idea
plugin.

Change-Id: Id7616987f5660911e951ddf20dacd4f407dacbd9
diff --git a/build.gradle b/build.gradle
index d1bd9cd..18b0ea2 100644
--- a/build.gradle
+++ b/build.gradle
@@ -2,6 +2,8 @@
 ext.releaseVersion = "0.3"
 ext.snapshotVersion = "0.3-SNAPSHOT"
 ext.androidPluginVersion = "1.0.0"
+ext.javaTargetCompatibility = 1.6
+ext.javaSourceCompatibility = 1.6
 
 subprojects {
     group = 'com.android.databinding'