[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
You may use several lines. I am not a 80-characters man, but this one could be easier to read on several lines. This remark applies to the whole file obviously.