Sort linkviews

This revives #770 which was reverted due to missing functionality in core.

We still need to wait for a core pr to get merged and a new core release before we can merge this.

@tgoyne @rrrlasse 
Replication for LinkView::sort() is done now and merged into master

On Thu, Sep 18, 2014 at 7:55 PM, Thomas Goyne <notifications@github.com>
wrote:

> In CHANGELOG.md:
>
> > @@ -108,6 +108,7 @@
> >
> >  ### Enhancements
> >
> > +* Add support for sorting RLMArray properties.
>
> Needs to be moved to the correct version.
>
> —
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> <https://github.com/realm/realm-cocoa/pull/918/files#r17743319>.
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