This implemenents create/read/update/delete/list for http triggers.
This isn't quite the final implementation: you can't look up old
versions by UUID since it only stores the latest update. I'll get to
that later.
FunctionStore uses fileStore for function code and resourceStore for
the Function's metadata. Environment- and HTTPTrigger- Store are just
thin wrappers on resourceStore.
There is probably a better way to organize this code, maybe with
reflection.