Add RotSprite algorithm for PixelsMovement (issue 121)

* Added app::RotationAlgorithm enum.
* Added app::ISelectionSettings::get/setRotationAlgorithm.
* Added app::SelectionSettingsObserver::onSetRotationAlgorithm.
* Added raster::image_rotsprite() function.
* Added ContextBar::RotAlgorithmField class to select the rotation algorithm.
* Now the mask isn't updated constantly on PixelsMovement::moveImage8),
  in this way when the user release the mouse button is when we recalculate
  the mask (to get better performance when the user is scaling/rotating
  the image).