Fix keyboard navigation in the dialog.
Issue #149
Add enable/disable methods to Editor and use them.
Use <button> instead of <div> for dialog buttons.
Issue #149
Merge branch 'dialog' of github.com:GoogleChrome/text-app into dialog

Conflicts:
	js/controllers/dialog.js
Stop keyboard event propagation when the dialog is open.
Merge pull request #209 from GoogleChrome/dialog

Implement keyboard navigation in the dialog
Close #149