Improve temperature-converter demo

[teobais]

We recently improved our temperature-converter demo to use JavaEE 8 and Wildfly, but there are still some JSF issues.

Improvements to be done:

• [ ] fix Kelvin conversion (only Celsius conversion works at the moment)
• [ ] replace radio button with a combo-box
• [ ] add Fahrenheit

[teobais]

@edburns maybe your help could be valuable here in case time allows during OC1.

[keilw]

Don't forget, the last one requires additional dependencies, either Unicode or Common Units from https://github.com/unitsofmeasurement/uom-systems