improved focusing of the notebook cell editors

[jonah-iden]

What it does

This improves focusing of cell editors in multiple ways:

• code cell editor will now recieve focus when clicking on the code cell status bar below the editor (the are showing python/markdown and the execution state)
• creating a new code cell now directly focuses the editor
• creating a new markdown cell now sets the cell into edit mode and focuses the editor
• when using shift+enter to execute and select next cell, the cursor does not stay in the previous cells editor anymore

How to test

open or create a new notebook. Test the cases listed above

Follow-ups

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[jbicker]

Works as described. Thanks!