Fixed units bug in k(T,P) equilibrium check error message.

Pressures are stored internally in Pa, not bar.
Sort reactants and products when loading reactions from CanTherm input.

Otherwise some bimolecular reactant channel comparisons could randomly
fail.
Fixed bug when saving PDepArrhenius kinetics in CanTherm.

The n parameter in an Arrhenius expression is a ScalarQuantity, so you
must use its value_si attribute to access its float value.
Deprecated use of frequency scale factor in CanTherm species files.

Previously you could specify the frequency scale factor in either or both
of the job input file or the species files, which is confusing and
redundant. I decided to keep the one in the job input file, since it
probably ought to be the same for all species in your job. A warning is
printed if this value is missing from the job input file or found in a
species file, to encourage users to make the change.
Added ScanLog class for loading/saving scan energies from a text file.

This provides the option of supplying the scan energies manually in a
text file instead of reading them from a Gaussian log file. The file is
also automatically saved by CanTherm when reading scan energies from a
Gaussian log file, in case you want to see or modify the results.

The file format is a two-column table with the angles and energies.
The units are read from the first line, and can take several values.
When loading, the energies will be offset so that the first value is
zero if not already done; this way you can provide the raw values in
Hartrees if you wish.
Can now specify mole fraction of excess reactant in Network.setConditions().

This is useful if you want to integrate the master equation or the set of
k(T,P) values forward in time. The solveFullME() and solveReducedME()
methods already account for the total concentration for bimolecular
reactions; thus this commit provides the ability to specify the mole
fractions.