Add WindowsStoreApp to .gitignore
Add WindowsStoreApp to .gitignore

Fixes #678.

HattMarris1/HoloToolkit-Unity,chadbramwell/HoloToolkit-Unity,out-of-pixel/HoloToolkit-Unity,willcong/HoloToolkit-Unity,davesmits/HoloToolkit-Unity,NeerajW/HoloToolkit-Unity,ForrestTrepte/HoloToolkit-Unity,darax/HoloToolkit-Unity,paseb/MixedRealityToolkit-Unity,paseb/HoloToolkit-Unity,HoloFan/HoloToolkit-Unity,dbastienMS/HoloToolkit-Unity