Update flipper to 0.11.0 and take advantage of the new features

What does this MR do?

Update Flipper to 0.11.0 and take advantage of the new features.

Are there points in the code the reviewer needs to double check?

• Added an ActiveSupport (using Rails.cache) caching adapter
• Overview of the new features can be found at https://johnnunemaker.com/flippin-features-at-runtime/
• Full Changelog can be found at https://github.com/jnunemaker/flipper/blob/v0.11.0/Changelog.md