This fix is a little ugly, but it’s the only simple solution without a
significant refactoring that restructures the relationship between
GraphQL/Validate and GraphQL/Resolve. The ugliness should go away if we
implement something like #2801.
* remove phase one/two distinction and hdbquery typeclass
* move extensions to default-extensions
* switch to LazyTx which only acquires a connection if needed
* move defns from TH module into Ops module
* remove tojson orphan instance for http exception
* remove orphan instance for dmlp1
* getTopLevelNodes will not throw any exceptions
