Jwt-helper

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* `"require": ["exp","iss"]` did not work as excepted. changed it.

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* fixed bug in `create_jwt`... i should write some tests

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* added `add_issuer` function to JWTValidator class

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* added `get_jwt_as_dict_untrusted`
* added `get_jwt_as_dict`

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* Initial Version
* Supports the following algorithms
* Symetric
* HS256
* HS384
* HS512
* Asymetric
* RS256
* RS384
* RS512