Restructure Edubuntu images as an add-on to Ubuntu

Edubuntu is currently released as a completely separate product with its own branding and communication requirements. This positioning comes with its own costs: it must be independently tested, which consumes significant amounts of time at each milestone, and it makes release communications more complicated and thus less likely to be absorbed by the target audience. There has been some discussion about repositioning this as an Education add-on pack for Ubuntu. Revisit this discussion, decide whether it is viable, and if so come up with an implementation plan.