support for UWP

[msadeh]

support for UWP Renderer

[stewartsims]

An adaptation of the iOS version can be made for a 'right-click to clear' version on UWP. See the following gist for the methods needed from a prototype I've done for this:

https://gist.github.com/stewartsims/248f7c8987aeed50d71f79934f85ae37

I imagine it would be preferable to add a clear button or modify the behaviour of the 'cross' on the UWP DatePicker but I could not find an easy way to do anything along these lines. Working with event handlers seems to be easier to do.