detect clicking on bkg of code cell
Update pioneer
Add bkNotebookCellModelManager to bkDebug
Fix #235, make delete cell undoable

After a cell is deleted, use Ctrl + z to undo. The history buffer size
is 1. Also any other cell operation that involves recreating cell map,
e.g. move up/down will clear the history buffer and void undo.
Fix #589, add 'other languages' menu item to new cell menu that pops up the plugin manager
determine if user clicked on top or bottom half of the input of the code cell background (harder than it sounds)
Fix #166, make tutorial links read-only
move cursor and focus on the text editor.  ignore if input is not showing.
Merge pull request #609 from twosigma/alee/fix-175

Fix #175, show error in UI when gist publish fails
Merge pull request #610 from twosigma/spot/466

clicking on background of code cell input area moves cursor
Merge pull request #608 from twosigma/alee/fix-166

Fix #166, make tutorial links read-only
Merge pull request #607 from twosigma/alee/fix-589

Fix #589, add 'other languages' menu item to new cell menu that pops up ...
Fix language indicators on cells

fixes #599
fixes #553
fixes #443
Merge pull request #611 from twosigma/sjs/fix-language-indicators

Fix language indicators on cells
Merge pull request #606 from twosigma/alee/fix-235

Make delete cell undoable
document ctrl-z
Fix #437, persist adv mode state in user pref
Merge pull request #614 from twosigma/alee/fix-437

Fix #437, persist adv mode state in user pref
expand R examples tut
add charting tut to table of contents, clean it up a bit