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
regarding this, I was wondering if you wanted to show some type of warning in the console if they are using the legacy option? (similar to what is being done for the npm changes)