Allow setting to disable logging decorators

[marc1uk]

Pleeease let's not force the addition of

\n[0]: 

on every message. I have never found this to be useful, and very often find it makes parsing logging messages much harder, with results like:

HWTRGLIST[1]:                                                                                                                 
[1]: known branches: {[1]}                                                                                                    
[1]: EVENTHEADER, HEADER, IDODXTLK, LOWE, MC, MU, ODTQLIST, SECONDARY, SN, TQAREAL, TQLIST, TQREAL, [1]: [0]: PrintEvent faile
d to get HWTRGLIST from Tree                                                                                                  
No such branch [1]: SOFTWARETRG[1]:                                                                                           
known branches: {[1]: [1]}[1]: EVENTHEADER, HEADER, IDODXTLK, LOWE, MC, MU, ODTQLIST, SECONDARY, SN, TQAREAL, TQLIST, TQREAL, 
[1]: [0]: PrintEvent failed to get SOFTWARETRG from Tree                                                                      
[1]:

just with a bunch of [x]: sprinkled randomly through my nicely formatted messages.
I could combine printed elements into one message first, but honestly that just makes printing logging messages a whole bunch more awkward, especially when combining printouts through if clauses or loops.
The fact that you hijack std::cout so that this happens even when the logging class isn't used is especially egregious.