Store gist text in database

[cheerfulstoic]

Could load the memory cache with the data from the database when the server starts up and then whenever we get back an etag result showing that it's changed we save it again. I worry somewhat about the scalability of loading all the gists into memory, so maybe the DB could be the only cache

[jexp]

On neo4j.org it was no issue, we can also easily compute how much the pure text of asciidoc gists costs in memory but I don't think it is a problem.