Some style cleanup for worksheet header; add ctrl+e/cmd+e to toggle edit mode
Fix edge case where old item was inheriting new_item state from a cancelled item
Edge case fixes and cleanup

- Update kbd shortcut modal
- clean up event propagation so save isn't called multiple times
- only call unInsert on esc if editing
JS cleanup

- standardize on 'handleKeydown' as function name
- insert an hr to separate tables when they get moved instead of a blank markdown line
- remove if/elses that are no longer necessary
- delete worksheet_interface_old.js file
correct mime type when downloading bundle files.

resolve issue #707
added word download and comments.
Merge branch 'refs/heads/upstream/master' into upstream/feature/worksheet_interface
Merge pull request #710 from codalab/feature/worksheet_interface

worksheet interface