Feature Manipulation APIs

[jng]

The Maestro API does not offer APIs for feature manipulation (insert, update, delete). The reason for this is that until recently, the default implementation of IServerConnection wraps the http mapagent that offers no such functionality.

Now that we not only have an implementation wrapping the official API, but also one wrapping mg-desktop, the time is right to offer the ability to insert, update and delete data as well as performing schema manipulations through standard interfaces.

[jng]

Fixed r6409. Includes new unit tests for mg-desktop wrapper