[ADD] slides gallery module

- Task: https://www.odoo.com/web?#id=9093&view_type=form&model=project.task
- Pad: https://pad.odoo.com/p/r.QlQTvBv6mCcMrK4B
there is a method to do that: https://github.com/odoo/odoo/blob/8.0/openerp/models.py#L5144