GLPI 0.83 compatibility
Makes plugin compatible with GLPI 0.83
Applied changes as documented in GLPI Plugins wiki to make it compatible with GLPI 0.83 code.
It is mostly methods/functions name/location changes.
Added licence informations (required by GLPI 0.83).
Dropdown tabs being now handled by GLPI itself, corresponding ajax/*.tabs.php files were removed.
Sets plugin version to 1.6.2.