Change duration _planned by planned_workload

htdocs/core/lib/project.lib.php

htdocs/core/modules/modProjet.class.php

htdocs/install/mysql/migration/3.4.0-3.5.0.sql

htdocs/install/mysql/tables/llx_projet_task.sql

htdocs/langs/en_US/projects.lang

htdocs/langs/fr_FR/projects.lang

htdocs/projet/class/task.class.php

htdocs/projet/index.php

htdocs/projet/tasks.php

htdocs/projet/tasks/task.php

htdocs/projet/tasks/time.php