Enhance open api capabilities

1. Add get single item interface
2. Allow passing the appendNamespacePrefix flag when creating public namespaces

Use DefaultHttpFirewall instead of default StrictHttpFirewall for apollo meta service to avoid 'The request was rejected because the URL was not normalized' issue.

使用DefaultHttpFirewall替换spring security默认的StrictHttpFirewall，用于解决客户端配置meta url时加上/，抛The request was rejected because the URL was not normalized.异常的问题

Fixes gray release issue #1677

use weak reference to hold bean objects so that they could be garbage collected

add @since annotation for recently added apis

增加EnvironmentPostProcessor处理，将Apollo配置加载提到初始化日志系统之前

fix the executing sequence of initializeSystemProperty

remove nicescroll

增加 Spring Boot 配置的方式eureka.service.url配置字段，方便利用kubernetes的ConfigMap方式

add active directory support

Fix #1609