Revert "units.js: Generate unit-based functions dynamically"

This reverts commit 07dd1f9b3d506a2121c2dc37a4f64b4ea3171b98.

Apparently this does not work since the generated functions all have
unit_type == 'altitude' ...
style.css: Fixed tooltips in flight list
units.js: Added documentation
units.js: Replaced this by slUnits

Be explicit, because "this" might not be equal to slUnits depending on the
calling context (e.g. flot).
units.js: Split conversion factor from formatter function
units.js: Moved the formatting call out of the convert() functions
units.js: Generate unit-based functions dynamically

Once again, but this time for real...
units.js: Simplified conversion functions in UNITS container
units.js: Added @expose directives for the closure compiler
units.js: Improved documentation

.. and moved the settings container below the constants
units.js: Simplified UNITS container

We don't need to save the format_decimal function for each unit, because
it is the same for all. The only difference is the number of decimal
places.
units.js: Adjusted method names to camelcase