[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
use one real binary field (image) and make image_medium and image_thumb as computed fields that only resize the original image (this exists in others modules)