finished porting plug-in to API version 2.0

- removed all QVariant returning functions - e.g. toString(), toInt(), toXXX() ... and QVariant() calls
- removed all QString references, replaced all QString methods (e.g. right(), length(), isEmpty()) by native Python methods
- changed QSettings return type where it occurred
- replaced QStringList with list
- replaced QList methods with native list methods (e.g. isEmpty(), count())
- replaced all SIGNAL/SLOTS with new style signals and connections

- replaced layer.select() and nextFeature() with QgsFeatureRequests and getFeatures()
- replaced QgsFeature attributes getters/setters
- removed/updated references to deprecated QGIS API methods, e.g. in QgsRubberBand (constructor,reset), QgsMapLayer (srs -> crs), QgsCoordinateReferenceSystem (epsg -> authid), QgsMapRenderer (destinationSrs -> destinationCrs)

- updated changelog and metadata

cf. http://hub.qgis.org/wiki/quantum-gis/Python_plugin_API_changes_from_18_to_20