[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
channel = 0 by default, what is the meaning of 0.id ? I think channel should be None by default; the check that it does exist before filtering on channel.id. Probably same remark about category.