message: Add select water, enlarge selectio and shrink selection
diff: #ifndef AVOGADRO_QTPLUGINS_SELECT_H
  #define AVOGADRO_QTPLUGINS_SELECT_H
  +#include <avogadro/core/vector.h>
  #include <avogadro/qtgui/extensionplugin.h>
  #include <avogadro/qtgui/pluginlayermanager.h>
  @@ -43,6 +44,13 @@ private slots:
  void selectElement(int element);
  void selectResidue();
  + void selectWater();
  + bool isWaterOxygen(Index i);
  +
  + void enlargeSelection();
  + void shrinkSelection();
  + Vector3 getSelectionCenter();
  +
  void createLayerFromSelection();
  private:
  