[Windows] Align API/props with Android and iOS

[asklar]

Feature request

With PR #157 the date picker now lives in the community repo. However there are some properties that are diverged:

• timeZoneOffsetInSeconds versus timeZoneOffsetInMinutes
• dayOfWeekFormat / dateFormat / firstDayOfWeek versus locale

We should align the APIs to be as close to android and iOS

Why it is needed

Apps that want to target Windows would have to fork their app code. This breaks the "Windows for free" goal of RNW.

Possible implementation

See PR 157