Add toolchain visibility setting #63
Description
Add a new setting that allows users to hide or show toolchains of their choice.
For example, users may not be interested in a specific toolchain and find it unnecessarily cluttering their feature table and other overviews such as the Feature Adoption Timeline.
Exception:
This setting must be ignored when the user visits the website with URL parameters, e.g., cppstat.dev?tags=cpp,gcc. This is to ensure that shared links always display data that is independent of the recipient's settings.