Fix compilation when log level >= LOG_DEBUG
Use statefs to manage context properties in Qt5 version

Centralize context property handling to class timed.
The context properties /com/nokia/time/time_zone/oracle
and /com/nokia/time/system_time/operational appear to
be obsolete, so they have not been ported to Qt5.
Merge pull request #24 from pgerdt/statefs

Use statefs to manage context properties in Qt5 version