Qgrid

- Fixes issue that made it impossible to set the value of a float cell to zero 174
- Updated tests to be python 2 compatible by removing usages of nonlocal. This change will help us to simplify the coda build process.

- Fixes issue where qgrid prevents all other widgets from working when used on Jupyterlab (154, 165)
- Adds new `sortable` and `filterable` grid options which allows users to disable sorting and/or filtering for the entire grid (164)
- Adds new `highlightSelectedCell` and `highlightSelectedRow` which allows users to change the cell/row highlighting behavior. Setting `highlightSelectedCell` to `True` and `highlightSelectedRow` to `False` will result in spreadsheet-style cell highlighting (in response to feedback on Twitter)
- Add `processPhosphorMessage` to handle resize events in Jupyterlab and when qgrid is embedded in other widgets. (169, 167)
- Trigger `_df_changed` event for filtering changes and edits. (170)
- Fixes an issue where the search text wouldn't be cleared in the text filter when the reset button is clicked

- Fix handling of `grid_options` in set_defaults https://github.com/quantopian/qgrid/issues/157

- Adds support for jupyterlab 0.30.x
- Uses a new stable plugin API that's available in jupyterlab 0.30.x
- Separate qgrid-jupyterlab npm package is no longer needed
- Issue with `set_defaults` fixed by https://github.com/quantopian/qgrid/pull/151
- Fix for deprecation warning that was appearing when committing edits on pandas 0.21.0

A small batch of changes to address a couple of issues:
- Fix column ordering issue on Python 2 (140)
- Display NaNs instead of blank cell for missing values (99)