Cancel during MaxEnt calculation in Muon FDA interface opens pop-up with too much text/info

[RichardWaiteSTFC]

Describe the bug

Clicking cancel button during MaxEnt calculation shows a pop-up with keyboard interrupt error text which is a bit off-putting!

To Reproduce (1) Follow instructions in Maxent Test

Expected behavior Would cancel the calculation and indicate this to the user in a more polished way that doesn't distract the use as much- e.g. grey the cancel button out