Add the possibility to update the alert while is visible to the user

[lechuckcaptain]

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Issue Info

Info	Value
Platform Name	ios
Platform Version	12.0
CFAlertViewController Version	3.1
Integration Method	cocoapods
Xcode Version	Xcode 10.1

Issue Description and Steps

It would be nice to have the possibility to change some alert properties dinamically, from a background thread while the alert is visible to the user (e.g. title, message).