[IMP] Manufacturing : Improved some usability issues.

Task : https://www.odoo.com/web#id=10541&view_type=form&model=project.task&menu_id=3942&action=327
pad link : https://pad.odoo.com/p/r.fZCshEnjNImVXxFn
why adding `<div>`'s in a form view... they shouldn't be necessary