Design team testing for dev.65

[samreid]

As a precursor to QA testing in #317, it would be nice for the design team to take a closer look at the latest version:

https://phet-dev.colorado.edu/html/wave-interference/1.0.0-dev.65/phet/wave-interference_en_phet.html

This has the following recent changes:
#316
#315

@arouinfar already reviewed a recent version, and signed off on subsequent changes. So @ariel-phet and @kathy-phet it would be great for you to take a look.

[samreid]

I also published dev.66 and opened a QA issue. If you are going to test, please use https://phet-dev.colorado.edu/html/wave-interference/1.0.0-dev.66/phet/wave-interference_en_phet.html

[ariel-phet]

Played a fair bit, overall things are looking good. Closing