[ADD] website: new countdown widget

- Task: https://www.odoo.com/web#id=8287&view_type=form&model=project.task
- Pad: https://pad.odoo.com/p/r.0coHaMolBpsxrIkg
Most of the part of CSS is for manipulating font-size with increasing / decreasing size of timer circle. Should I keep it the same ?