Add Admin verification. If an Admin user wants to acccess the api it does not ne...

[todo]

https://github.com/Gewaer/gewaer-cms-api/blob/f97d17334e58e9c9c78a9f8729df6c510f8afc51/library/Middleware/SiteMiddleware.php#L41-L46

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This issue was generated by todo based on a @todo comment in f97d173 when #2 was merged. cc @gewaer.