Make value change handling for experiment creation more lightweight

[priyald17]

Currently, each text box and check box in experiment creation has its own anonymous value change handler. This could become a performance issue once there are multiple input groups. So, for classes with multiple ValueChangeHandlers (e.g. InputsPanel), let the containing class be the ValueChangeHandler.

[priyald17]

Upon re-evaluation, it seems that this isn't that big a gain in speed because ValueChangeHandler and ValueChangeHandler calls need to be handled either separately or with a lot of casting. For now, will leave value change handling for inputs as is.