Deprecate analytics.js-integrations

[ndhoule]

Deprecates analytics.js-integration in favor of individual integration repositories over in https://github.com/segment-integrations.

Don't merge this yet; we need to push analytics.js live using the new integration repositories and port over all existing issues.

[sperand-io]

analytics.js-integrations :)

important distinction as the individual repos still extend the base @ http://github.com/segmentio/analytics.js-integration

[ndhoule]

Ah yeah, typo. My b