Change glossary terms to use explicit tags placed by hand

[NathanLovato]

Glossary terms are currently automatically detected in the content. This is the cause of several issues, false positives, repeated highlights, but also issues like #1063

The way to control that and provide a good experience is to instead pick the terms to highlight and provide a tooltip for by hand. This task is a reminder to do this effort (someday, as time allows).