Remove un-needed dependency libs.
For runtime, only gson & slf4j are needed.
Test libs have no need to be placed here.
Add nullable from javax.annotation;
Move log4j.properties to test resources, it is only for testing.
For production env, app service should have it's own log4j properties file, or use other logging framework.
Update a pom plugin.
Add feature: ios notification category support.
Seperate unit test and integration test.
mvn test will only execute unit tests.