This also seems to squash a stubborn space leak we see with
subscriptions (linking to canonical #3388 for reference).
This may also fix some of the "Unexpected exception" websockets
exceptions we are now surfacing (see e.g. #4344)
Also: dev.sh: fix hpc reporting
Initial work on this done by Vamshi.
* 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
