add video thumbnails
Merge pull request #479 from code-dot-org/staging

DTT: add video thumbnails
remove aws files that popped up from levelbuilder
DTT
Upgrade 5 front-ends at a time.
Merge branch 'production' of github.com:code-dot-org/code-dot-org into test
Dropbox changes
add callouts to new hourofcode script
Dropbox changes.
Merge pull request #481 from code-dot-org/test

DTP
Email tweaks
Hide the new stuff from the dashboard.
Dropbox changes
Wording fixups for Frozen launch.
Merge branch 'staging' into frozenlaunchlinks