Feature: Add administrator's config

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FreeOTPPlus is a great tool, we however would like to make it more business atractive by adding security to it.

This new feature adresses the problem when we would like to restrict the user's available features.

We would enjoy to have in the settings menu an extra item called admin settings, this could be password protected (or a 6 digit pin for) upon entering the correct pin or password, the administrator can select the options available to the end user. So all the previous options available or not.

Thanks for making this application even greater than before.

Eric