It must be possible to set the expression language for input and output entries (all cells of the table body, except annotations)

Questions to answer

• How does the workflow look like to open a combo-box where you can set the expression-language (context-menu on the cell, where to open the popup, styling, ...)
• Design an indicator for cells which have an expression language set
• Ideally, the indicator can listen to events (e.g. is a node in the DOM), so that you can open the combo-box edit when clicking on it.