[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
I agree with you, as this is an helper function to crop images, this could go in openerp.tools or in an util class in website module