Log to STDERR only when necessary

[david-bouyssie]

Currently GLOG outputs INFO messages to STDERR.
This can be misleading for command line users.

This issue is already reported as a comment in the code.
See raw2mzDB.cpp:

write logs to error output (GLOG does not write on standard output, but why ???)

GLOG has not been designed to output messages to STDOUT and I think it won't change.

Because we already have a lot of boost dependencies it might be worth to consider to replace GLOG by the boost::log library.
Here is the doc: https://theboostcpplibraries.com/boost.log

boost::log seems to support this feature:
https://stackoverflow.com/questions/21380530/boost-log-to-file-and-stdout-simultaneously