add dav4droid support part1

test_client/build.gradle

@@ -43,4 +43,8 @@ android {
     packagingOptions {
         exclude 'META-INF/LICENSE.txt'
     }
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
 }