Use defaultTemperatureUnits instead of defaultCelsius and add control to the Options dialog

[arouinfar]

In #216 we created the defaultCelsius query parameter to set the default temperature units to Celsius. This query parameter has never been shared with users in the Teacher Tips or with PhET-iO clients in phet-io-guide.md.

In greenhouse-effect we created a similar query parameter defaultTemperatureUnits that takes values of F, C, and K, see phetsims/greenhouse-effect#186. This approach is preferable because we now have validation of query parameter values. This pattern also translates better into a user-facing control in the Options Dialog.

Next time this simulation is published off of master let's make these changes @jbphet:

• Deprecate defaultCelsius in favor of defaultTemperatureUnits
• Add corresponding RadioButtonGroup to the Options dialog

This applies to both SOM and SOMB.

[jbphet]

Sound reasonable. This sim, I believe, is slated to have its phet-io implementation updated to the latest and greatest reasonably soon. I'm going to defer this particular issue now, and when the sim is getting some focus for the phet-io update, we can undefer and implement.