Enhance left bar with action buttons

[damiendevienne]

Hey!
Here are a few problems identified on the left buttons that would help with navigation :

• would be nice to add mouseover action. From top to bottom:
  zoom in / zoumer
  zoom out / dézoumer
  home / accueil
  search a taxa / rechercher un taxon
  itinerary / itinéraire
  get a subtree / sous-arbres
  display additional data / données additionelles
  get a snapshot / capture d'écran
  parameters / paramètres

• when one clicks on one of the buttons (e.g. search), it opens a new div on the left. To close it, it is necessary to click again on the same icon. THis could be enhanced in two ways:
  -modify the icon clicked so that we know which one is active
  -add a small x top righ of the div to be able to close it this way as well