[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
Ugh ? Shouldn't that kind of method 1/ be check and verified 2/ be commented to explain its purpose 3/ be at model level ?