Object logging

This MR introduces per-object specific logging, so that e.g. all logs generated by the same modem object are all prefixed with the same "modemX" string, e.g.:

ModemManager[270221]: <debug> [1585674972.744424] [modem0] enabling +CCWA call waiting indications in primary port...
ModemManager[270221]: <debug> [1585674972.744456] [modem0/ttyACM0/at] device open count is 4 (open)
ModemManager[270221]: <debug> [1585674972.744483] [modem0/ttyACM0/at] device open count is 3 (close)
ModemManager[270221]: <debug> [1585674972.744511] [modem0/ttyACM0/at] --> 'AT+CCWA=1<CR>'
ModemManager[270221]: <debug> [1585674972.757003] [modem0/ttyACM0/at] <-- '<CR><LF>OK<CR><LF>'
ModemManager[270221]: <info>  [1585674972.757183] [modem0] state changed (enabling -> enabled)

This change is extremely useful when analyzing daemon logs on systems with more than one modem.

The MR doesn't fully port all the codebase yet, but it already ports all the main base objects.