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.