Client : query only the displayed region in the QuadTree visualization

Signed-off-by: Jean-François Erdelyi <jean-francois.erdelyi@etu.iut-tlse3.fr>
Resolves-bug: https://github.com/sebhtml/Ray-Cloud-Browser/issues/14
Merge branch 'master' of git://github.com/Djeef/Ray-Cloud-Browser