Fix worksheets when preview mode is active
Merge pull request #417 from javierluraschi/FixWorksheetsPreview

Fix worksheets when preview mode is active
Refactor base.html and app.html
Merge branch 'RefactorBaseApp' of https://github.com/javierluraschi/codalab into dev
Merge pull request #418 from javierluraschi/RefactorBaseApp

Refactor base.html and app.html
removed bundles directory
merged upstream changes
Merge pull request #425 from percyliang/master

removed bundles directory
Use getattr to read Preview_Worksheet setting.
Merge branch 'master' of https://github.com/codalab/codalab into dev