Support for multiple template repositories

A working first stab at support for multiple template repositories. Main aim is to allow for internal company repositories so that company specific templates needn't pollute the public repository.
basically we need that one spot over in TemplateCacheActor to deal with all the downloading and error handling, so that may involve refactoring in some way to avoid the earlier need for the name field, or allow the download code to set the name field, or something. We never want to "transparently download" in a place that may not handle the errors etc. correctly.