Investigate unknown/unclear sources for information presented in previous Guide 2017

[mgreiler]

In the previous guide (2017), which can be found here https://owasp.org/www-project-code-review-guide/assets/OWASP_Code_Review_Guide_v2.pdf, are several graphs and very interesting statements and facts that do not have proper attribution of source.

For example, in Figure 1, a survey result that is only very briefly mentioned is depict. The quality of this source, and its legitimacy needs to be investigated. Based on what the investigation finds, we either will keep, remove or update the information for the upcoming version of the guide.

Information and statements that are hard to judge given the information in the guide can be found throughout. Each one of those has to be investigated and evaluated for future-fit in the updated/new guide.

Each piece of information that needs to be investigated and evaluated should probably become its own issue. This issue can serve as a "parent" issue.