Steam node from tea kettle looks fairly lame

[jbphet]

The steam node's appearance could be improved with some better drawing code. Here's what it looks like now:

[chrisklus]

I made a small change to improve the steam visual. If we have time, or after version 1.0, we can go back and construct the stem and cloud a little differently.

I also added a TODO for using dt in the step() method so that the steam looks consistent across all platforms.

[chrisklus]

I've implemented new steam for the tea kettle using a pattern similar to the beaker's steam. Assigning to @jbphet for code review, and feedback from anyone @ariel-phet @arouinfar @jbphet.

Dev version with this change and the change in #178: https://phet-dev.colorado.edu/html/energy-forms-and-changes/1.1.0-dev.3/phet/energy-forms-and-changes_en_phet.html

I did some testing to see if this has negative performance impacts. On my machine, the tea kettle steam and beaker steam running simultaneously shows 60 FPS for the old steam and new steam. On Jemison, our slowest iPad (4th gen), the same test ran at about 9 FPS for the old steam and 10-13 for the new. Visually, the performance looks the same. I also tried out the new steam on one of our better iPads, and it was running nicely.

[arouinfar]

@chrisklus I really like the new steam node! It looks smoother and more realistic to me.

[chrisklus]

Thanks @arouinfar!

[ariel-phet]

Looks very nice to me as well!

[jbphet]

That's a big improvement in the appearance, and the code looks great. Closing.