[WIP] adding config flags to control all items mentioned in PRIVACY.md

closes #3241
- in config.js, the `tinfoil` attribute holds all privacy-related flags
- `tinfoil: true` disables everything (equivalent to setting all flags to false)
- updating config.example.js with commented-out flags and description


Once this is merged in, http://support.ghost.org/config still needs to be updated with the new config options
Putting this in here to see how folks feel about it.
My goal was to provide a way to notify users of a config property that will soon be deprecated.