[WIP] Adding Carthage support

[rynecheow]

Adding Carthage support by creating MotionAnimator.framework target with it's scheme shared so that Carthage is able to find and build the shared scheme according to what is defined in the scheme.

By correctly exposing the public headers and hiding the private headers, this will also tell Xcode to build and include the correct headers available to library consumers.

Pre-requisite:

1. Adding Carthage support motion-interchange-objc#45 is merged
2. New tagged version is released on https://github.com/material-motion/motion-interchange-objc

[codecov]

Codecov Report

Merging #126 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #126   +/-   ##
========================================
  Coverage    87.92%   87.92%           
========================================
  Files            9        9           
  Lines          613      613           
========================================
  Hits           539      539           
  Misses          74       74

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2cafc9e...18c07b9. Read the comment docs.