Allow sidebar to be resized

So that full names can be visible:

<img width="432" alt="image" src="https://user-images.githubusercontent.com/928367/196700065-b7cdaf94-cf54-4869-8d6f-3ef4a08c09ba.png">

Would be nice to store the size in localstorage and load it from there if present to keep it consistent for a given browser session.