factorized document actions

Conflicts:
	htdocs/societe/document.php
form to link a file
links sql table
rename parameter to rowid
bugfix
Link class with CRUD methods
link creation in dol_add_file_process
new attributes
display links
factorized form attach, documents list and links list for the document pages
UI
delete function for links
typo
don't try to create a link when the link input field is empty
add a field for label input
translations
edit link lines function
translation
code formating
open link in new tab