Provide option for "Interrupt Running Evaluations" in REPL status bar menu

[lspector]

The "Calva: Interrupt Running Evaluations" command is super handy for anyone working on problems that typically involve long-running computations or infinite loops (which may be intentional or not).

It seems to me that it would make sense to provide this as an option that appears when clicking on the "REPL ⚡" button in the status bar. This would make it more discoverable and easier to invoke. My sense is that this command is of general enough interest, and useful enough especially to beginners, that putting it in the UI would be a good idea.