…984)

* begin work

* enable testing on 4 react versions on travis
* enable local testing on 4 versions
* enable running wallaby if installed

* Fix tests in 0.14, 15, and 16

* remove 15.4, not really necessary and it requires a tweak to the install script

* fix 2 major potential issues

1) by putting all the installs in setupTestEnv into a single npm command, npm --no-save becomes possible. When they are on separate lines, the 2nd npm i removes the previous line's work
2) after test runs, we restore the node_modules to what devDependencies says

* update contributing docs and add missing test:watch

* re-work to use subdirectories for testing specific react versions

caveat: collecting coverage does not work yet, we need to combine the lcov reports

* fully working! with merged coverage!

* fix linting, remove unnecessary file

* fix test:watch

* fix travis tests to run in parallel for each version

* oops, didn't make travis run the CI test

* sigh... npm syntax error

* speed up test suites by only installing the specific version needed

* remove unused plugin

* simplify test script options in package.json

use the REACT env variable to run tests for a specific version, set it to "all" to run for all supported versions

* simpler gitignore

* remove unnecessary coverage merging, codecov does that automagically

* simplify test running

* new docs on testing specific React versions

* move scripts to test/, remove unused dep

* revert unintentional cosmetic changes

* add default version for "npm test"

* revert unintentional cosmetic changes to test import order

* restore the correct test renderer version

* fix travis, add a note about the matrix needing update on adding a React version

* Add cross-spawn dependency

* Use cross-spawn for consistent NPM installations cross-platform