List all templates (MVP)

[bartolomej]

Modify an existing /v1/templates endpoint to retrieve all templates instead of throwing an error, if name query parameter isn't provided.

This is technically a breaking change, so if we'd wanna merge this to the main repo, we'd need to move this logic to v2 endpoints added here: onflow#28

This isn't an ideal solution for a few reasons:

• this same endpoint now returns either a list of templates, a single template, or an empty value (if using the name query param)
  • it could be a more flexible approach to let it only return a list of resources. In that way, this could be a general purpouse search endpoint, possibly supporting multiple query params and always returning a list of search results.
• always returning all snapshots in the database, may not be a scalable solution long term
  • it should be fine for now, as there are only a couple hundred templates available (when counting the seeded ones only)