(refactor) upgrade to react 16

[potench]

Goal:

Update to allow React 16 as a peerDependency.

Changes:

1. react 16 as a peerDependency
2. react 16 as a devDependency with all tests passing.
3. tests should still pass with react 15
4. using react-test-renderer for ShallowRenderer tests now

Notes

1. Replaces Allow React 16 #57
2. To test against React 15, first update package.json: devDependency, reminstall node_modules, then npm run test

// 1. manually update "package.json: devDependency" 
"react": "^15.0.1",
"react-dom": "^15.0.1",

[codecov]

Codecov Report

Merging #60 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #60   +/-   ##
=======================================
  Coverage   92.93%   92.93%           
=======================================
  Files           8        8           
  Lines         580      580           
=======================================
  Hits          539      539           
  Misses         41       41

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