Move database logic into separate subdirectory

I'm trying to see if this speeds up builds a bit. May not without a
module boundary, but for now it's nice organization to have as the
program grows.

sql/oauth_by_user_id.sql

@@ -1,3 +0,0 @@
--- OauthTokenByUserId
-SELECT * FROM oauth_token WHERE
-	user_id = $1;