Disabled components should be pickable

[jessegreenberg]

It has been part of the code review checklist to make sure that user interface components with enabled:false also have pickable:false. For accessibility, we need disabled components to be pickable so that they can still be discovered with the mouse or finger.

We will need to go through interface components and make sure that elements have pickable:true while disabled. If we set pickable to true for any component, we should verify that nothing has been broken and that performance was not negatively impacted in sims which use the changed element.

[jessegreenberg]

This issue is dependent on phetsims/scenery#41. If we can get the accessible DOM to handle discoverability, pickability is no longer an issue for accessibility.

[pixelzoom]

Disabled components should now be using scenery's new inputEnabled option instead of pickable. It will take some time to update all UI components that are currently using pickable, but see #257.

@jessegreenberg Can we close this issue?

[jessegreenberg]

Yes, this issue can be closed now. We will have to follow through with phetsims/scenery#41 for discoverability.