Require Atom 0.116

Now that the React editor is the default, require the latest version of
Atom (dart-tools uses the React decorations API).
Don't load chokidar until absolutely required.

Seems to cause random failures.
Don't listen for events unless this is a dart project.

This is a bit of a hack. Need to fix later.
Update to use latest decorations API.
Some more whack refactoring.

Push decorator code into its own component so it can track changes.
Refresh decorations.
Fix up parsing of dartanalyzer output.