Show service status in the UI

[Kaljurand]

For services that support this (e.g. the service that is based on kaldi-gstreamer-server) present the status of the service (number of available slots, latency, etc.) somewhere / under certain conditions, e.g.

• add a live message into "Settings/Recognition services/K6nele (fast recognition)" showing the number of currently available slots (similarly to http://bark.phon.ioc.ee:82/dev/duplex-speech-api/static/status.html), or a network error message;
• after 2 consecutive network error messages in the IME / voice panel, test the network, and if it's otherwise working then pop up a dialog blaming the server, possibly offering the email address of the server maintainer as a target for complaints.

Motivated by #48

[Kaljurand]

Improved in https://github.com/Kaljurand/K6nele/releases/tag/v1.6.90