[RFC] Generic form type and possibility to inject "settings manager"

[takeit]

To be able to define more settings (e.g. adding google analytics id, changing theme, google adsense, enable extra converter statistics etc.) generic form type needs to be created which can be used by other applications.

It should be also possible to provide custom "settings manager" (in bundle's configuration) from 3rd party apps which should take care about management and persisting settings.