Include authorship/copyright notes and address code overlap

[yoelcortes]

Most modules in the thermosteam.properties subpackage and a couple of modules elsewhere originated from thermo. Although most have been enhanced/altered, it is important to credit the original author. To address this issue, a comment header will be added to each copied/modified file noting the origin, authors and license. Also, all authorship, date, and license information will be removed from the module docstring and be placed as a comment block for both consistency and keeping the documentation concise.

Additionally, it may be possible to contribute back the enhancements made to these files to the thermo repository and use thermo as a third-party dependency for better code reuse and management. Alternatively, it is also possible to work with the original author of these files to create a lower-level package that can work as a better dependency for thermo, thermosteam, and other packages.

[yoelcortes]

The copyright, license, and author attributions have been added to all files. Currently working with the author of thermo to release a manageable, standalone, lower-level package to serve as a better dependence for thermosteam.