FB bundles wrap warning() calls in __DEV__
Split dev-mode transforms into separate parts:
1) umd+cjs+fb: Wrap warning calls with process.env checks
2) umd+cjs: Replace error messages with minified codes
Also updated transforms to use __DEV__ since it transforms to smaller code after stripEnvVariables is run.
Also renamed 'scripts/error-codes/dev-expression-with-codes.js' -> 'scripts/error-codes/replace-invariant-error-codes.js'
* took codes.json from the 15-dev branch
* fixed react:extract-errors task in gulpfile
* generated error codes
* Revert "generated error codes"
This reverts commit b8f3aeed9d8f0d469edd5f6623fa6090930594d8.
* Added a README for the error code system
