* Support over 3 states in LayoutAdapter
* Allow to inherite FloatingPanelState
* Support a custome FloatingPanelState in ObjC
* Replace Menu enum with UseCase enum in Samples.app
* Rename UIExtensions to Extensions
* Add CustomState use case in Samples app
The default Swift version leaves 4.0. Because it avoids build errors
with Carthage on each Xcode version from the source compatibility
between Swift 4.0, 4.2 and 5.0.
With regard to CocoaPods, the pod spec is going to support
`swift_versions` introduced in CocoaPods v1.7.0. For now, a user needs
to override `SWIFT_VERSION` appropriately in Podfile.
Shin Yamamoto