[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
some access rights are missing here: because here, only the admin can create a channel or edit a category... people that have rights of website edition should also be able to manage slides