Set extension-api's defaultConfig.

The Android Gradle plugin prefers to use these values instead of the values in AndroidManifest.xml, and it will always ignore the manifest's `minSdkVersion` even without `defaultConfig.minSdkVersion`.

dependencies/extension-api/build.gradle

@@ -14,4 +14,9 @@ apply plugin: 'com.android.library'
 android {
 	compileSdkVersion Integer.parseInt(project.ANDROID_BUILD_SDK_VERSION)
 	buildToolsVersion project.ANDROID_BUILD_TOOLS_VERSION
+	
+	defaultConfig {
+		minSdkVersion Integer.parseInt(project.ANDROID_BUILD_MIN_SDK_VERSION)
+		targetSdkVersion Integer.parseInt(project.ANDROID_BUILD_TARGET_SDK_VERSION)
+	}
 }