Add logging messages

Add debug/info and error messages using the logging tool from gancio. It's in /server/log.js Specially, to capture exceptions from telegraf. It uses the debug() tool, that has just one logging level.

Example:

// path: /server/example.js
const log = require('./log')
log.info("starting")
log.error("not good")

ref https://framagit.org/les/gancio/-/blob/master/server/notifier.js