Update _ Windows Store UI.txt for Win 8.1

Win 8.1 doesn't have LayoutAwarePage anymore
Merge pull request #605 from RobGibbens/v3.1

Update _ Windows Store UI.txt for Win 8.1
Merge branch 'v3.1' of https://github.com/rvuistin/MvvmCross into v3.1
Issue607: check that environment actually supports API Level 11
Merge pull request #611 from rb1234/Issue607

Issue607: check that environment actually supports API Level 11
Merge remote-tracking branch 'origin/v3.1' into v3.1