Reduce number of reference categories

With the new reference page aliases are grouped by addin for every category. From a user perspective it would be more useful to have less categories, which group aliases from multiple addins and built-in, than categories for every addin (e.g. `EntityFramework` / `EntityFramework 6`, `Argument` / `Arguments`, etc). This would require PRs to the different addins and Cake itself to cleanup used categories.

Start by reviewing the reference page's current alias grouping and the categories named in the issue, including EntityFramework, EntityFramework 6, Argument, and Arguments. Then identify where categories are defined across the Cake website, its addins, and Cake itself. Done means the reference page presents fewer user-oriented categories that combine built-in and addin aliases, with the required changes prepared across the affected projects.

Written by the indexing model from the issue text.