Add syncthingctl to toltec

[mooomooo]

Package information
syncthingctl (from https://github.com/Martchus/syncthingtray)

Reason for addition
This is a CLI that orchestrates syncthing, which is already in the repo. With it, it'd be possible to configure / manage syncthing via an on-device terminal, without needing a browser or another computer on the same network to access the web interface.

[palfrey]

#957 is an early hack towards this, but it's a hard build. See notes there.

[Martchus]

Note that Syncthing itself also provides a CLI. It has a different focus than syncthingctl so both tools complement each other. Maybe the CLI of Syncthing itself is good enough for your use case.