Able to grab an object when inputEnabledProperty is false

[Nancy-Salpepi]

For phetsims/qa#1136 and related to #368, when a moveable object's inputEnabledProperty is set to false
-the grab cue is still there when using alt input
-it can still be grabbed but not moved with both mouse and alt input

Even though it is a slightly different interaction, I looked at MSaB and when the balls are disabled, I can't grab the ball and the grab cue isn't there. Only the solid interactive highlight is present.

[zepumph]

Working on this now.

[zepumph]

Fixed above, can you please confirm? You should still be able to focus it, but you cannot interact with it.

[Nancy-Salpepi]

Working great! Closing.