Add a way to export and import Sonar configuration with an xml file

The goal of this functionality is to be able to export and import all kind of configurations an administrator can do through the Sonar web interface.

So, this export / import mechanism should include :

• Columns displayed in the Sonar homepage (with default sorted one)
• Does the treemap need to be displayed in the Sonar homepage ?
• Which are the default axes of the TreeMap ?
• All plugins configurations
• All manuel metrics definitions