Added a batchSize for feedback

The batch size limits the number of tokens emitted with the `feedback` event as they are received. A 0 value indicates that tokens will be passed after they have all been received.
Fixed notification.retryLimit behaviour.

As described in issue #142 the behaviour when retryLimit = 0 did not match the documentation.
Don't set "aps" key if no well-known properties are present

Fixes #141
Fixed a possible crasher as seen in #139 / #141

Credit: Romain Goyet (Ecco)