THERMR changes for S(a,b) files

[whaeck]

The following are changes to be made to thermr when processing S(a,b) files to improve consistency:

1. The sb value used for S(a,b) normalisation is calculated using the B(1) value in the LIST record of the S(a,b) ENDF file and the natom value which is on the thermr input even though this last value is also given in the ENDF file as B(6). To be consistent, natom should be read from the ENDF file instead (a message should be issued to signal that natom on the input is not equal to the one in the ENDF file).
2. To solve some of the normalisation issues encountered when using older S(a,b) files with newer unbound evaluations, the B(1) value should be replaced by a value read from the reconstructed unbound nuclide at the S(a,b) cut-off energy, at least when these values are significantly different. At the very least, thermr should issue a message stating that both are inconsistent.
3. Add an inorm input parameter (values of 0 and 1) on card 2 after iprint. inorm=0 will be the old NJOY2016 behaviour (calculate sb from B(1)) and inorm=1 will be the proposed sb normalisation change (using the value read from the reconstructed unbound nuclide at the S(a,b) cut-off energy).

These changes are relatively simple to make but will require extensive testing.