perf: index.html bypasses app engine concurrent access limit

We need to leverage index.html as much as possible since app engine spawns instances when parallel java based requests occur. We have some bugs that we need to fix to handle that also (work in progress).

We should discuss SEO next time we get a chance. I'm thinking we can have dedicated backends for SEO so that front-end performance is not handled. And if the backend.jsp sees that the request is not escaped it redirects to the html file.