Tab and enter end text editing and move right, down respectively

Fixed delegate setup to be consistent and use the existing delegate method for both cases (double click to start editing, just start typing to start editing). Use the notification info to figure out which way to move the selected cell and do that after persisting the edited data.

Fixes #13.

![](https://dl.dropboxusercontent.com/s/6qrby8rf475e7q4/486B5E99-0F74-443E-9152-8220617D232A-53540-000171E58523615F.gif?dl=0)