Add unit conversions to age, dimension, temperature

[chrimc62]

With $units we know enough to be able to automatically convert dimension units, i.e.
$units = feet, convert kilometer, hectometer, inches, etc. and vice versa.
We can also convert areas and perhaps as a bonus currency although that requires an API call to an exchange. I suspect the best way to do this is to create some custom LG functions to do the conversion, i.e.

# convert(entity, desiredUnits)
- SWITCH:
- CASE ${'Inches')
    - SWITCH ${entity.units}
    - CASE ${'Inches'}
  ...

and perhaps 
# canConvert(entity, desiredUnits)

Then we can use those in the generated dialogs to convert units automatically or complain about not being able to convert. For example if $units = Inches.

"3 feet" would automatically be converted to "36 inches"
"3 square meters" would complain "expected inches"
etc.

We also need to add combination logic, i.e. "6 foot 1 inches" results in this:

"dimension": [
        {
          "number": 6,
          "units": "Foot"
        },
        {
          "number": 1,
          "units": "Inch"
        }
      ]