More Compact UI for specifying visual encoding

[kanitw]

Now

• [x] allow manually resize

Later

• [ ] Allow empty shelf to be a text input on click that have a pop up autocomplete to select field

• [ ] Design question: if there is already a field. How do we enable both removing a field and changing a field.

• [ ] media query equivalent for screen-size ...

[saulshanabrook]

We started some mockups for more limited Voyager views in Jupyterlab.