Prefer organizationDomain or CFBundleIdentifier for settings file

Prefer organizationDomain or CFBundleIdentifier for settings file

Watch for attempts to write to "Trolltech" preferences and use
QCoreApplication::organizationDomain() instead. If that doesn't exist,
then fall back to CFBundleIdentifier if possible. If that doesn't
exist, then follow the old code path and use the hardcoded string.

This change eliminates extra files being created which helps Mac app
store acceptance.

Change-Id: I1ba3984b46cf3888f371d87f6ad8ea6c2f26d2ec
Reviewed-by: Morten Johan Sørvig <morten.sorvig@nokia.com>