[IMP] remove sheet from the forms which are used for configuration

Remove sheet from the forms which are used for configuration.
Improved some ugly form views.

[Pad] : https://pad.odoo.com/p/r.VOFr7Zt1UDND0T3F
[Task] : https://openerp.my.openerp.com/web#id=6091&view_type=form&model=project.task&menu_id=3942&action=327