Defines molar volume to be zero. Density remains defined as being
per unit area or length, depending on the dimensionality of the phase.
Also fixes setting surface composition using mass/mole fractions so
that the sum of concentrations always equals the site density.
Partially resolves#1312
* test-clib: species-specific three-body reaction are reformatted
* test-cxx/test-f90: reformatted species-specific three-body reactions;
change of spurious net reaction rates, which should be zero
* test-f77-ctlib: change of spurious net production rate for AR (gri30)