Add import suite file from file system feature

The same pull request with https://github.com/cbeust/testng-eclipse/pull/95

I already updated my solution based on the comments.

could you help me review it? the screen shot as follow:
![image](https://f.cloud.github.com/assets/1169277/1112290/db5a9e50-19d7-11e3-82ec-232ea695cee2.png)