Bug fixes for ArcGIS WebApp Builder beta 2

Fixed:
- Configuration experience: layer selection changing on it's own when
dropdown is clicked.
- Configuration experience: symbols chosen are now remembered within the
same session.
- Attribute Editor: not showing fields in beta 2.
- 'Zoom to' and 'Maximize' button in feature popup not restored when
widget is closed; buttons showed all feature popups now.
- Cleaned up no longer used code/files.
Merge pull request #13 from adrwhong/master

Bug fixes for ArcGIS WebApp Builder beta 2