Serverpython: python plugins for QGIS server

Python plugins for QGIS server implementation.

A cmake config variable activates the server plugins support: **MAPSERVER_HAVE_PYTHON_PLUGINS**

Plugin currently implemented hooks:
requestReady ()
responseComplete ()
sendResponse ()

The plugin filters are available in the request handler and more hooks can be easily added if they are needed in core services.

Annotated bindings API: http://www.itopen.it/qgis/serverplugins/api/annotated.html
Example plugin: https://github.com/elpaso/qgis-helloserver