[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
@rim-odoo . yes we should remove @api.multi here. 
@rga-odoo : we should improve demo data if any issue.