Do not required dsme to be running when mce starts up

Previously mce could not be started unless dsme was running and was
forced to exit if dsme stopped/crashed.

Now mce tracks availability of dsme by watching D-Bus name ownership
changes of com.nokia.dsme on system bus and makes connection when
dsme is up and running.

While dsme is not available process watchdog ping-pong based heartbeat
activities do not get triggered and shutdown requests can't be made.

I/O errors during socket IPC with dsme trigger re-connect attempt.

Also the mce --debug-mode command line option is removed since it is not
needed anymore.

[mce] Do not required dsme to be running when mce starts up. Fixes JB#11581
Use common prefix for functions internal to mce-dsme.c
Use common prefix for global functions defined in mce-dsme.c
Identify mce version & flavor on start up

So that both DSME and MCE versions can be found from journal.
Merge pull request #184 from spiiroin/track_dsme

Track dsme availability