BNL license text approved by Dorene.

To be merged to each diffpy package repositories.
Use Columbia for source started at CU.

Fix year for an earlier source files.
Fix Columbia Trustees name and copyright year range.
Fix header texts to uniform format.

Also, use a common product name libdiffpy.
Rename LICENSE.txt to LICENSE_DANSE.txt.
Fix BSA BNL name in file headers.
Add BNL license text.

Merge branch 'license' from diffpy-release.