Minor BugFix : Wrong variable reference in getNomUrl 

Display of Category Url was incompete due to reference to "$ref" instead of "$label"
Minor BugFix : Compatibility of function getNomUrl 

Using Ref & Label for Category Name display is necessary for compatibility
Missing Key for getNomUrl function
Missing Key for getNomUrl function
Minor BugFix : Missing thumbs folder in Category Images List

Sub-folder for thumbs was missing in category image list, url was wrong....
removed "thumb\" subdir addition 

Category Image Thumb sub-folder now directly added by function liste_photos
Avoid missing class error for fetch_thirdparty method
Not need to test if class exists with require_once
includes and show_documents
no dol_include
Fix : tva not coming from multiprice
Merge pull request #2008 from ndrosis/patch-10

Fix : The tva not coming from multi price for invoice
Fix: Graph report rubbish information. Better to have them as option.
Merge branch '3.6' of git@github.com:Dolibarr/dolibarr.git into 3.6
Minor BugFix : Missing delete Category Multilangual fields

Delete of Multilangual fields was missing, impossible to delete category.

Fixed Error : 
Cannot delete or update a parent row: a foreign key constraint fails (`Dol-3.6`.`llx_categorie_lang`, CONSTRAINT `fk_category_lang_fk_category` FOREIGN KEY (`fk_category`) REFERENCES `llx_categorie` (`rowid`))
Minor css enhancement
Qual: Skeleton class updated by using table_element instead "mytable"
and __METHOD__ for syslog
Fix: Removed unused property
Fix: Removed warning
Merge branch 'develop' of git@github.com:Dolibarr/dolibarr.git into develop