Pyramid-facebook

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* Added `CanceledOrder` when any payment update fail during event notification.
* add includeme for any sub module to uniform configuration
* facebook auth policy does not rely anymore on context for authentication.
* add an `CanvasRequested` event triggered when a identified user request
canvas.

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* In credits: Check item title not being an empty string to avoid FB failing with
no explicit message. "Fail early."
* Fixed bug which raised configuration conflict because `pyramid_facebook` was
not commiting config via `config.commit`.

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* Initial version