From Patrick Ohly <patrick.ohly@intel.com>

Like instant messaging handles, email addresses can be assumed to be
unique for individuals. Therefore they can be used for linking by
default. This commit enables that in the EDS backend.

With email addresses being a linkable property, delaying loading of
them no longer makes sense because they will always be loaded.

Closes: https://bugzilla.gnome.org/show_bug.cgi?id=685401