[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
rename this method to `increment_counter`, the name will be more explicit (a method name should always be significant by itself, it has already to tell me "this method does this operation")