Make corrections to tar and soot model

Makes some corrections to the tar and soot model implemented in ODT.

1. Use correct rate expressions based on a revision to the original reference (Josephson et al. Revision to Modeling Soot Derived from Pulverized Coal. 2016).
2. Adds an H2 source due to soot formation from tar. In most cases, we assume tar has the empirical formula CxHy and soot is purely carbon, so when tar reacts to form soot, a source term for H2 due to this reaction should be present.
3. Use correct units for Avagadro's number for soot oxidation rate computation (1/kmol rather than 1/mol).

This merge request also adds the option to compute species diffusivities based on a unity Lewis number assumption. This option is activated by specifying DetailedTransport: False in the input file. A test named simple_species_transport has been added to test this new option.

Lastly, tar and soot oxidation reactions are now disabled when the gas phase chemistry model is set to cold_flow.

Any test involving gas phase transport where coal models are enabled will fail, and are listed below.

• simple_species_transport (new test)
• singleParticle
• particle_coldflow
• particle_hc
• particle_x_velocity
• particle_size
• CCK_single_particle