[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
Do you really need to use 2 different IO libraries in the same file (`io` and `cStringIO`)? I think you could try to use only one