Tidy up thermo comments in chemkin files.

-Removed unecessary declaration line '! Thermo Comments:'
-Added 'Thermo library:' label to thermo originating from thermo libraries.
-Removed the NASA fitting to Wilhoit comments because they clutter up the comments
Tidy up kinetics comments in chemkin files.

-Removed unecessary declation of '! Kinetics comments:'
-Fixed labeling of exact rate rule matches (was falsely labeling some kinetics
as estimates when they were actually exact matches)
-Removed extra line with reaction string using original names.  The chemkin
reaction string should be sufficient.
-Removed line commenting on flux pairs (generates clutter and not super useful)

Concern:
- When merging RMG models together, a lot of comments will be duplicated.
This should be fixed later.