Update delete method (WIP)
Refactor adding items and deleting items. Restore click-to-focus functionality
Merge pull request #655 from codalab/feature/560-delete-worksheet-items

Feature/560 delete worksheet items
Insert markdown improvements, permissions flag

- Insert a markdown item before or after current focused item
- re-consolidate markdown on save
- if inserted item is escaped out of with no content, remove the item from the array as well as the DOM
- improvement for keyboard shortcut propagation
- add edit_permission boolean to ws_obj.state that controls insert, edit, and checkboxes (delete)
#628, #656