Included provision for unregister of user

Updated destroy method (#38)

* Updated SDK to include BACKGROUND_REFRESH policy for actions

* Updated ReadMe for BACKGROUND_REFRESH

* Add Destroy method

* Included methods to clear cache

* Updated url end point

* Updated regions with correct values

* Refactored

* Updated read

* Updated Readme

* Removed unused files

* Updated send metrics api to send only the metrics array

* included support for boolean and integer for custom attributes

* Refactored

* Fix to ensure that existing custom parameters update the user registration

* Fix to ensure default json for cached parameter is empty

* Updated ui for in app messages

* Updated destroy method