TFJ-753 added property "isRetweeted" to Status and LazyStatus.

Added **isRetweeted** property to *Status* interface and implemented to build that property value from JSON, and added testcases.

The content of this pull request is same as that pull request:  https://github.com/yusuke/twitter4j/pull/86
https://github.com/yusuke/twitter4j/pull/87