Expose deviceIdentifier

[rodrigoelp]

Changes included here:

• Expose the deviceIdentifier as provided by Bugfender, used to uniquely identify an instance out in the field.

• Changed the location of the bugfender framework, as node_modules is usually not committed to a build repository, it prevents a commit to be valid across multiple computers. To solve this, the location of the bugfender.framework should be changed from ./node_modules/react-native-bugfender to ./ios/frameworks

• Included typescript type definitions making the library useful to those doing development with a strongly typed language. This type definition also works as documentation of the code.

• Updated the readme file to give it a bit more structure and include the same for the deviceIdentifier() method.

[RubenVot]

Nice work!
Be aware that the last versions of BF will be returning an URL for the device identifier instead of a hash. We are going to include this soon in the official SDK for react native.
We accept PR and feature proposals there as well :)