Data sources support in diff_stix

[isaisabel]

As a user of diff_stix, I want the script to be able to summarize changes in data sources and data components.

Update diff_stix to include data sources and data components. Data components should be nested beneath their data sources using the same logic as sub-techniques and techniques.

[jondricek]

Admin note: closing all remaining issues and pull requests prior to archiving the repository