Enable automatic time/timezone update from cellular network time

Add oFono-based cellular network information classes, which provide the functionality that the closed source Harmattan CellularQt used to provide.

These classes do not contain any code from CellularQt, only the interface has been partially replicated based on docs from http://harmattan-dev.nokia.com/docs/platform-api-reference/xml/daily-docs/libcellular-qt/

Note that not using ofono-qt is intentional, even if the code would be a little shorter with the library. Not using ofono-qt leaves the option to moc DBus interfaces in unit tests (to be added in a separate commit), and gives more control of error logging.

A network time plugin needs to be added to oFono to make the code in this pull request to work, the corresponding changes to oFono are reviewed in: http://review.merproject.org/#change,1057