Displaying local-time for locations in city-view

Set one time-label. Set its value using timezone information and
GLib.DateTime. Update its value using GnomeWallClock whenever it
needs to get updated. Diconnect the notify::clock during world-view.

https://bugzilla.gnome.org/show_bug.cgi?id=705050
Adding feature to show weather conditions for current location

Use Geoclue to get the current place and find nearest weather station
using it and find_nearest_city method of GWeather-location. Add this
current location if the location does not exist already in the
world_view. Don't add location to 'locations' value of settings. To
handle this use one more column named AUTOMATIC that shows whether
location is added automatically or not. Check this column on removing
the location and if it is true then remove that 'iter' and return.

https://bugzilla.gnome.org/show_bug.cgi?id=704268