Update GUI.js

added an 'id' for the container of the collapsible panels, to allow to add new custom panels. In the near future I'll post an example on how to add a custom panel.
Merge pull request #89 from luca76/patch-1

Allow to add custom panels on the LeftPanel
Create contextMenu.css

 - for the black text in the context menu items (otherwise they will be red)
Update qgiswebclient.html
Update WebgisInit.js

 - Added context menu support for layers in the layerTree
 - Added "Zoom To Layer Extent" context-menu item
Update Translations.js

 - added new strings for Context menu item
 - updated remaining untranslated italian strings
Update README.t2t

Added my name to Developers and Translators
Merge pull request #5 from luca76/master

merge from luca76 for layer context menu