Sends notifications for default filename changes.

This fixes linting.enabled, for example.
Fix JSHint error
Project prefs no longer apply to files outside the project.
`PreferencesManager.set` now handles contexts the same way as `get`
Last bit of cleanup.

* Changed `Editor.optionChange` event to send Brackets preference names
* Updated the doc comments for the editor options functions in Editor.js
* Fixed setValueAndSave to use the new behavior.