New project templates

@devoncarew
cc: @umop

This ~ gets us to where we've discussed. For all web apps, I haven't moved the sources from `web` subdirectory to the top level, mostly to be consistent across all app types as possible. But tell me if you still want that done.

With this PR, all the publicly visible templates (the ones not under the new 'wip-project-templates' dev flag) work out of the box, including the JS Polymer element's demo.

I still have a tiny bit of refactoring to do in the template instantiating code, but that's orthogonal to the templates themselves, and will be done in a separate PR.