* Implement click-to-open for babel syntax errors in build error overlay

* Add click-to-open support for lint errors and refactor parser

* Reactor code to reuse open-in-editor functionality in both build and runtime error overlays

* Fix some eslint warnings

* Add a comment about keeping middleware and dev client in sync

* Remove es6 features from webpack dev client

* Make open-in-editor functionality to work with new iframe script

* Rename `openInEditor` to `editorHandler`
 -  Remove indirection of openInEditorListener
 -  Check editorHandler for null before styling error clickable

* Fix flow errors