Feature/split view command/js

[cybermerlin]

added the ability to set the css class style icon in SplitViewCommand

[msftclas]

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[cybermerlin]

src/js/WinJS/Controls/Flyout.js:
line 1372 col 56 (W116) Expected '!==' and instead saw '!='.
line 1393 col 100 (W116) Expected '!==' and instead saw '!='.
line 1402 col 100 (W116) Expected '!==' and instead saw '!='.
3 lint errors

I do not change this file. Merge please this request.