units.js: Moved code into slUnits module
baro.js: Added @expose markers for the closure compiler

We don't use it yet, but maybe in the future we will.
units.js: Moved init() function below local variables
units.js: Only overwrite defaults if necessary
units.js: Fixed variable names

constants should be UPPERCASE
variables should be lowercase
units.js: Remove unnecessary format_number() function

Calling format_decimal() without setting the decimals parameter results
in the same thing.
units.js, units.py: Adjusted decimal places for speed and lift units
units.js: Merged UNITS definitions
units.js: Added settings dict
units.js: Generate unit-based functions dynamically