#1 Units for parameters and variables

[ciroki]

Develop a new class daeUnits to replace units in daeVariableType currently given as a plain string.
It should support all operators and functions supported by daetools and Latex/MathML export.
It should be based on 7 SI base units and derived units.
Think about using the boost.units library.
adNode and adNodeArray classes should be updated to support units consistency checking