feat(ids): add localStorageFallbackDisabled flag

[f2prateek]

This adds a flag localStorageFallbackDisabled to disable the localStorage fallback code.

localStorageFallbackDisabled is falsy by default, hence the fallback code is opt in by default, and requires opt out.

Since the configuration for users and groups are supplied seperately, to use this you need to pass in:

analytics.initialize(settings, {
  user: {
    localStorageFallbackDisabled: true,
  },
  group: {
   localStorageFallbackDisabled: true
  }
})

[nhi-nguyen]

analytics.initialize(settings, {
  user: {
    localStorageFallbackDisabled: true,
  },
  group: {
   localStorageFallbackDisabled: true
  }
})

Two questions:

• Is there a situation where users may want to call do this outside/after initialize?
• related to the above, is there any value in writing this in a helper function?