PrintHelper + Code printing

[deltakosh]

PrintHelper allows developer to print a XAML control per page (no page break).
You can easily create any kind of xaml (like textboxes, rich text or even images) and send them to the printer with a few lines of code:

var printHelper = new PrintHelper(Container);
printHelper.AddFrameworkElementToPrint(PrintableContent);

printHelper.OnPrintFailed += PrintHelper_OnPrintFailed;
printHelper.OnPrintSucceeded += PrintHelper_OnPrintSucceeded;

await printHelper.ShowPrintUIAsync("UWP Community Toolkit Sample App");

This PR also includes a Print button to print code samples (Fixes #450)

Documentation will come in another PR

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[IbraheemOsama]

LGTM but there are conflicts @deltakosh
I was wondering if there is a cloning method we can call on PrintableContent so we don't have to remove it from root grid and readd it after printing succeeded.
(I didn't find my self but maybe serialization and deserialization would cause a loop because of parent child relation)

[deltakosh]

Unfortunately there is XamlReader in UWP :(

[deltakosh]

Should be good now

[IbraheemOsama]

@deltakosh sorry but we still having conflicts here :)

[deltakosh]

lol everytime I merge other PR I add more conflicts here :)

[deltakosh]

@IbraheemOsama should be good now

[hermitdave]

when changing the page orientation from portrait to landscape, the preview hangs and in debug mode we get this error

An exception of type 'System.ArgumentException' occurred in mscorlib.ni.dll but was not handled in user code

Additional information: An item with the same key has already been added. Key: Windows.UI.Xaml.Controls.StackPanel

[deltakosh]

fixed! Thanks @hermitdave

[hermitdave]

LGTM