Should categoryName be required when adding a SoundGenerator?

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soundManager supports putting sounds into named "catagories". But when a SoundGenerator is added, specifying a catagory is optional, via option catagoryName. For example:

soundManager.addSoundGenerator( goBackSoundClip, { categoryName: 'user-interface' } );

Because categoryName is optional, this can lead to oversights like phetsims/vegas#98.

Should categoryName be required? Should it default to something that is not null, so that all sounds get put in some "default" category? Is there a reason why every SoundGenerator should NOT be in a category?

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Here's the current state of addSoundGenerator calls. There are zero uses of categoryName in sims, and common code is using it inconsistently. This seems like a good argument for making categoryName required, and standardizing on some categories other that 'ui-sounds'.

sim	calls to addSoundGenerator	use of categoryName
balloons-and-static-electricity	8	0
circuilt-construction-kit-common	1	0
faradays-law	9	0
fourier-making-waves	1	0
friction	9	0
gravity-force-lab-basics	5	0
gravity-force-lab	5	0
greenhouse-effect	19	0
inverse-square-law-common	3	0
john-travoltage	7	0
molarity	3	0
ohms-law	3	0
quadrilateral	3	0
ratio-and-proportion	8	0
resistance-in-a-wire	1	0
wave-interference	8	0

common repo	calls to addSoundGenerator	use of categoryName
joist	2	2
scenery-phet	1	1
tambo	1	1
vegas	6	1

[jbphet]

We discussed this in today's design team meeting and decided to add the GameAudioPlayer sounds into a category, and have sounds for which no category is specified go into a default category. I will do that work.