See #32. Working version with PreviewView extending (React)EditorView.

Closes #31. Shows line numbers.
Fixes #25. Font-size syncing (automatically by EditorView).
Fixes #27. Theme syncing (automatically by EditorView).
Fixes #44. Exceptions and crashes should no longer be an issue.
See #32. Remove TextBuffer depdency to fix building package. Apply workaround.
See #32. Reimplement preview debouncing.

Also cleaned up console.log and other misc code.
Closes #32. Reimplement showing messages (loading and errors)

Complete implementation of PreviewView extending EditorView.
Fixes #32. Cleaner requiring of Atom internal modules.

Instead of forcing React to be enabled and
requiring the exported modules from require('atom')
use the resourcePath from atom.config.resourcePath
and build the absolute path to the Atom internal modules
and reqire them directly.
Merge pull request #45 from Glavin001/use-atoms-react-editor-view

Closes #32. PreviewView now extends ReactEditorView.