Input errors that kill the app

[AngusMcLure]

Making a list of inputs that kill the app. Can perhaps split these into separate issues, but perhaps easier to make a checklist here for the minor/easy ones?

• [x] Disconnects if 'Catch mean' > 'Catch variance'. Instead, it should return an error saying that 'Catch variance' needs to be higher than 'Catch mean'
• [x] Disconnects if 'Cost unit', 'Cost pool', etc. is negative. Instead, it should return an error saying that 'Cost X' needs to be 0 or greater
• [x] Fails to produce a result (though doesn't disconnect immediately) when all costs are set to 0. Runs for a long time and it doesn't seem possible to interrupt it. Instead, it should return an error saying that at least one of the costs should be greater than 0 to choose an optimal design.

I can add more to this list as I find problems (or open separate issues if we prefer?)

[fredjaya]

Fine to add to the list for now, maybe open as separate issues once a bit more stable!

[fredjaya]

All done, except need to implement:

• [ ] The same UI and input validation for when "Other" settings are selected (bad inputs = remove Run! button)