Add XEP-0070: Verifying HTTP Requests via XMPP support

[cmeng-git]

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[Flowdalic]

I usually do not add new features to stable Smack branches, so please adjust the target branch to master.

[Flowdalic]

First round of review. I think especially the manager design needs to be changed.

[Flowdalic]

Suggested change

	private final String url;
	private final URI url;

I believe this member should be of type URI.

[cmeng-git]

Can this variable be handled as a string all the ways. Otherwise need to do extract steps during xml phrase() and in toXML() method.
In aTalk app implementation, the value is used as string in prompting user to accept or reject the auth request. Do not see the need for app to access the URL directly.