- Replaced the old free-hand tool for defining the AoI, for one that reads from the current extents:
 - user enters page and the current maptool is immediatly set to zoomIn()
 -  user zooms to the desired extent (he can also use the QGIS zoom tools); if he wants to reset the zoom, he can go nack to the previous page; if he is happy, he can press "next"
 - in the validatePage event, the following actions are triggered:
  - a memory layer is created and one single feature is added to it; this feature is a polygon, instantiated from the rectangle tha defines the current map extent;
  - the clip algorithms are called (as before) and the new layers are added to the view
  - the new layers are styled using the qml files