Feature request: Add a "stopping" state to the button in the top right

[SaintSampo]

Right now the button has three states:

• CONNECT XRP
• RUN
• STOP

When you stop a running program, there is at least a few seconds where the user has no feedback, but can still click the button, until the program actually stops and the state returns to "RUN". The user experience would be better if there was an additional "stopping" state where the button was unactionable.