[ task #814 ] Add extrafield feature into Project/project tasks module

htdocs/core/lib/project.lib.php

htdocs/core/modules/modProjet.class.php

htdocs/install/mysql/migration/3.3.0-3.4.0.sql

htdocs/langs/ca_ES/admin.lang

htdocs/langs/en_US/admin.lang

htdocs/langs/es_ES/admin.lang

htdocs/langs/fr_FR/admin.lang

htdocs/projet/admin/project.php

htdocs/projet/admin/project_extrafields.php

htdocs/projet/admin/project_task_extrafields.php

htdocs/projet/class/project.class.php

htdocs/projet/class/task.class.php

htdocs/projet/fiche.php

htdocs/projet/tasks.php

htdocs/projet/tasks/task.php