Dilate Pointer Areas Around Wave button?

[KatieWoe]

I noticed that, when using an iPad, it seemed like pushing the button to start the wave didn't always work. I looked at the touch pointer areas from those button and they look pretty small. I think it might be useful if they are a bit bigger. We'd have to be careful that they don't overlap when separation between two sources is as small as possible, but even a slightly larger target might be useful.
For phetsims/qa#238

[arouinfar]

Great suggestion @KatieWoe! This is the worst case scenario for the Interference screen, which should still leave ample room for dilation of the touch area around the on/off button.

@samreid seems like we could make the touch areas pretty generous here. Let's try something like this:

This touch area would apply to the source on/off button for all scenes/screens.

[samreid]

Here's a dilation of 8 view coordinates:

Pushed and ready for review, @arouinfar can you please take a look?

[arouinfar]

Looks good to me @samreid! @KatieWoe can you try this out on an iPad?

[KatieWoe]

Looks good on the Waves and Interference screen. Not implemented on the Slits screen. Do we want it to be @arouinfar?

[samreid]

That was not intentional, self-assigning to fix that up.

[samreid]

Proposed fix pushed, @KatieWoe can you please double check and close if all is well?

[KatieWoe]

Looks good in master.

[arouinfar]

Not implemented on the Slits screen. Do we want it to be @arouinfar?

Good catch @KatieWoe! Thanks for taking care of it @samreid.