[Toaster] First design proposal - building non-Git layers

[Barros Pena, Belen]

Hi all,

I've put together an initial proposal to cover the following requirements

* get Toaster to build layers not set up as Git repositories
* build without Internet connectivity.

The design proposal is explained in this video

https://youtu.be/N6gvTtZUP3Y

I hope it's not too boring.

This is just a starting point: the goal of the video is to kick off a
discussion on how to enable this functionality. Things can change as much
as needed, so don't be afraid of expressing concerns, asking questions,
making alternative proposals or saying that you don't like it at all.

I've organised a design review meeting as follows:

Date: July 7th 2016
Time: 4pm BST / 8am PST / 8:30pm IST
Tel: 1-888-875-9370
Bridge: 4
Passcode: 1434913

Until then, feel free to send your feedback / questions by replying to
this thread. I am away for a couple of weeks from tomorrow, but I will
collect all feedback on my return. If you can, please also attend the
design review, since decisions are made there that you might care about,
and the review is your best chance to have your say.

Thanks!

Belén