Windows 10 1511 Release - March 2016 Update 3

• smalltile-sdk.png and squaretile-sdk.png assets rescaled to appease WACK. Sorry it took so long. We're developers, not graphic designers.
• BasicSuspension: Upgrade SDK version to 10586. (Missed this in the migration, sorry.)
• FileAccess: Use TryGetItemAsync to check if a file exists.
• XamlNavigation: Updated with new visual design.
• XamlPullToRefresh: Reimplemented to take advantage of Windows.UI.Composition.