minor refactor and add more ut

2 抽离了一个公共父类ApolloProcessor，用来处理反射相关的逻辑。 ApolloJsonValueProcessor,ApolloAnnotationProcessor,SpringValueProcessor都继承它
3 在PropertySourceProcessor中注册自动更新的监听器AutoUpdateConfigChangeListener
4 SpringValue增加isJson字段，表示这个属性是否是Json类型的
5 增加了单元测试

use ApplicationContextInitializer instead of SpringApplicationRunListener for better compatibility

Refresh session & add admin pages entry point

Auto Updating Spring Placeholder Values

2. Support XML config placeholders
3. Add more tests to cover all kinds of cases
4. Update apollo demo to adapt for auto update functionality

add nested property test

add xml config test for PR #962

Multimap并未严格保持@EnableApolloConfig注解中namespace定义的顺序。

update code style

minor fix