Various improvements to tracing & diagnostics. (#1707)

* Various improvements to tracing & diagnostics.

- Manage possibility of `Account` not having code for `PodAccount`
- New RPC: `trace_sendRawTransaction`
- See raw transaction dump when inspecting over RPC

* Fix test

* Remove one of the dupe error messages

* Remove unneeded `&`s

* Reformat and extremely minor optimisation

* Minor optimisation

* Remove unneeded let

* Fix tests.

* Additional fix.

* Minor rename.

[ci:skip]

* Bowing to the pressure.