Architecture v2

[davidcassany]

Re work the architecture page, it should be updated to provide a better overview

[agracey]

We should also build a graphic that explains the full stack and put it on the overview page.

If needed, we may be able to pay a designer to make it pretty (and animated?)

[davidcassany]

Closing there is already a first iteration of the architecture documentation. Specific issues should be opened for missing details.