Pass-through mode

**Overview**
Add an additional button that simply executes the code in the cell instead of generating the chatify UI.

**Describe the solution you'd like**
It seems like something as simple as this could work:
- Add a button or menu to the UI where the user can select something like "remove UI and run this cell"
- Pressing the button does two things:
- Removes the `%%explain` command from the current cell
- Calls `exec(contents)` on the cell's contents

**Other things to think about**
- What's the right interface for this? A button? An additional tab + dropdown menu option? Something else?