[Toaster] Building non-Git layers - Final design now available

[Barros Pena, Belen]

As usual, design documentation is attached to the corresponding Bugzilla
entries

https://bugzilla.yoctoproject.org/show_bug.cgi?id=9911
https://bugzilla.yoctoproject.org/show_bug.cgi?id=9913

The main features are also prototyped at:

http://www.yoctoproject.org/toaster/b3/import-layer.html
http://www.yoctoproject.org/toaster/b3/layer-details-dir.html

The above hopefully includes all the information needed to build the
feature.

Any questions, comments or missing details, please let me know.

Thanks!

Belén