mainWindow: check that placeStore name is not null
placeStore: remove last reference to dirty
placeStore: sort store by ascending added time

https://bugzilla.gnome.org/show_bug.cgi?id=722825
placeStore: do not throw exception in store

https://bugzilla.gnome.org/show_bug.cgi?id=722825
Update recent added time on re-visit

https://bugzilla.gnome.org/show_bug.cgi?id=722825