Add ReactHostHolder interface to provide access to ReactHostDelegate

Author: hebertcisco

android/app/src/main/java/com/microsoft/codepush/react/ReactHostHolder.java

@@ -0,0 +1,11 @@
+package com.microsoft.codepush.react;
+
+import com.facebook.react.ReactHost;
+import com.facebook.react.runtime.ReactHostDelegate;
+
+/**
+ * Provides access to a {@link ReactHostDelegate}
+ */
+public interface ReactHostHolder {
+    ReactHost getReactHost();
+}