Add `SwitchFeature`, rebrand `FeatureToggled` and performance improvements

💣 Breaking changes

• FeatureToggled and render (func) is now only invoked when feature matches
• children on the other-hand is invoked with isFeatureEnabled in any case
  • This matches behaviour in react-router
• Anywhere you used variate you should now use variation
  • We used the wrong terms here sorry for the confusion

🚬 Deprecations

• FeatureToggled got renamed to ToggleFeature
  • FeatureToggled will be supported for some time but using it will give you a warning

🌟 Features

• SwitchFeature is new component rendering the first matching ToggleFeature
  • It hope to ease so called multi variate testing by ensuring that only one feature is rendered at a time

<SwitchFeature>
   <ToggleFeature flag="foo" variation="bar" toggledComponent={MyFeature}/>
   <ToggleFeature flag="foo" variation="baz" render={() => <p>Turned on</p>} />
   <ToggleFeature flag="foo" variation="bar">
       { ({ isFeautureEnabled } ) => <p>Turned on?: { isFeatureEnabled }</p> }
   </ToggleFeature>
   <ToggleFeature flag="foo" variation="foo" toggledComponent={MyFeature} untoggledComponent={DisabledFeature}/>
</SwitchFeature>

🥇 Fixes

• ConfigureFlopflip is now more mindful about not triggering wasteful renders
  • All of its unrelated state is extracted away from React to speed up your app
• ConfigureFlopflip and the underlying FlagSubscription had a hairy infinite configuration loop
  • The needed mix of componentDidMount and componentDidUpdate in pair with configure and reconfigure lead to a repeated brute force configuration of adapters which yielded a stack overlow
  • While fixing the bug we improved our internal state handling from naive boolean flags to more descriptive enums
• Wrapping of displayNames is now removed for all components
  • This makes snapshotting more consistent between releases
  • It eases testing with enzyme (a wrapper.find('ToggleFeature is enough)

💘 Tooling

• Dependencies have been updated again making sure flopflip is compatible with React@16.2