Cut 0.9.19 release

Should include:

Support for Firmware 1.3.5 https://gitlab.hax0rbana.org/public-repos/signet/signet-base/-/issues/4 (see release process in signet-base for what to do)
Updated terminology #31 (closed)
Correct update/help URLs #25 (closed)

All other issues are optional.

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