Modification

1. Adding the required expressions into 'Restart' variables, which will be saved automatically for restart. As a result, the tests will fail because more fields are saved now.
2. Modifying the method for giving particle loadings for coal particles. Two methods are provided. One is giving fuel-air equivalence ratio in the input file by Particles: FuelAirEquivalenceRatio:'. The other is giving particle loading directly in the input file by Particles: {ParticleLoading: ParticleLoadingInflow:}'. For the second method, the equivalence ratio is not required to be given in the input file.
3. Solving the problem about stof: out of range when setting Fields based on database for restarting. Using std::stod, instead of std::stof will solve the problem.
4. Adding CCK model for char reactions.