Settings: Add support for settings only available for developer mode

[Lypsolon]

Story

as a developer i want to disable some functions in an add-on but this will never be useful for a User.
i would like to add some developer options to an add-on that have default values and are not available if the bundle is not in develop

Problems

currently all settings for add-ons need to be visible all the time. but developers might eg: want to disable bin download. a feature like this would only clutter the settings interface

Proposal

allow settings to define if they are only Visible if the bundle is in Development Mode