Cookbook: Hotkeys for faster notebook editing

When working with the HTML notebook, it is hard to quickly navigate when editing a cell, as Page up/down Pos1 and End keys only work inside the current cell. Jumping between cells requires the mouse. This can be especially annoying, because outside of code cells (no cell selected or a markdown cell), the keys work as is usual in the browser.

Currently hotkeys are not configurable, so this patch for codecell.js and notebook.js gives the following behavior:

Page up    - move one cell up
Page down  - move one cell down
Ctrl. Pos1 - jump to first cell
Ctrl. End  - jumo to last cell

The changes are available here: https://github.com/juhasch/ipython/compare/cell-hotkeys

The patched files can be installed in the static/js directory of the user profile, so the IPython installation is not modified.