Allow server to include add-ons when running in sketch mode

[kadamwhite]

Is there any reason not to always load all core P5 add-ons? cc @brysonian @lmccart -- I feel that it's easiest if e.g. we just auto-included p5.Sound, rather than toggling them on with a flag e.g. --addons, but if you're aware of any reason not to include core add-ons please let me know. I may be missing something.

[brysonian]

I can't think of a reason not to load them all. The only thing is that maybe a user would start here and then incorporate a sketch into another webpage without including all the add ons, and then be confused about why the code isn't working. But i don't think that case would be helped by not including them all by default. A better solution would be to encourage people to add require('p5.sound) to their sketches to use the sound lib, simply as a way to more clearly declare the dependency.