Make Fitting Tool frame wider on OS X so "Stop" button in Confidence panel is visible by default

[jbudynk]

If a model has many free parameters and a user tries to calculate the confidence interval, it may take a long time (> 30 seconds) to calculate. The user may want to stop the calculation.

Either add a new "Stop" button for the confidence intervals, or give the fitting "Stop" button functionality to stop confidence interval calculations.

[jbudynk]

Nevermind -- on OS X, the Fitting Tool window is too narrow, and so I couldn't see the stop button. Widening the window let me see the Stop button.

So instead of adding a "Stop" button, the Fitting Tool window GUI should be updated so that the "stop" button always appears by default.