adding stubs for 500 or 503 pages
feature(templates): generate static 500 error pages with a grunt task
Merge pull request #913 from mozilla/issue-690

Static 500, 503 error pages

This looks great @zaach! Thanks for working through it with me.

r+

@mostlygeek - does nginx need to be updated to respond with the static 500.html page if the node server for some reason stops responding?