Preloader support for StaggeredGridLayoutManager

[oleksii-iermolenko]

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Currently ListPreloader only supports the LinearLayoutManager Added support for the StaggeredGridLayoutManager, which is also quite a popular layout manager.

[google-cla[bot]]

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[sjudd]

Thanks for the contribution. Are you up for signing the CLA?

[oleksii-iermolenko]

Thanks for the contribution. Are you up for signing the CLA?

I did already :)

[oleksii-iermolenko]

@sjudd any updates on this?