Suggestion: split up main "sales" site and year specific site.

[mietcls]

We suggested to have a "year specific" site and a "sales" site for the next editions. This would mean summerofcode.be (or osoc.be) has all the information about signing up, what it is, who it's for, some fancy projects highlighted, ... and the year specific website like 2019.summerofcode.be (or 2019.osoc.be) shows all the projects, people, partners, pictures and practical information for that edition.