Servatrice: group all the use of QSettings in a single file

and add a method to guess the path of servatrice.ini
win32 NSIS installer: uninstall servatrice*

just avoid deleting servatrice.ini, if the user manually made one from
the servatrice.ini.example
Fix logfile option in servatrice.ini

servatrice was using hardcocded filename “server.log” even if a custom
value was specified
Servatrice: Add a default option for every config value

add an empty room swell, if none had been defined in the config (or we
are running with no config at all)
win32: Avoid wiping server.log on upgrade
servatrice: as a third choice, check for a config in /etc/servatrice/
use 4 spaces instead of tabs
use qWarning instead of std::err
Merge pull request #346 from ctrlaltca/servatrice_win32

Servatrice win32 fixes