Trace signals conditionally exposed

[maackle]

PR summary

• Rename Signal::Internal to Signal::Trace
• Add expose_trace_signals bool to Configuration, if false then Trace signals will never be emitted over any interface
• Set expose_trace_signals to true for nodejs conductor config

The first commit is noisy, it's just the sweeping rename to Trace. Look at the second commit for the actual filtering logic

changelog

Please check one of the following, relating to the CHANGELOG-UNRELEASED.md

• this is a code change that effects some consumer (e.g. zome developers) of holochain core so it is added to the CHANGELOG-UNRELEASED.md (linked above), with the format - summary of change [PR#1234](https://github.com/holochain/holochain-rust/pull/1234)
• this is not a code change, or doesn't effect anyone outside holochain core development

[zippy]

This is good, but tests broken and need to be updated.

[zippy]

Hey @maackle what's the scoop with this PR, should we be moving it forward?

[maackle]

I redid this one as #1428 since my first attempt at find-and-replace was overzealous.