Glossary + keyword tags

This MR adds glossaries and keywords to Wax and to JATS export as requested by Amnet.

In the front matter, there's a keyword section, with "Keyword list" and "Key word". This expects a paragraph tagged as a keyword list, with keywords inside it tagged as key words:

Key words: key word 1, key word 2, key word 3

The whole paragraph is the key word list; "key word 1", "key word 2", "key word 3" are the key words.

If this exists in Wax, when JATS is exported, the key words in Wax override any key words that are found in the form.

In the back matter, there's a glossary group of tags. A glossary section goes around a list of glossary items. For a glossary item to be valid, it needs to have a glossary term selected inside it. A glossary section may also have a title. So a glossary section could look like this:

Glossary
**term 1** Term 1 means this . . .
**term 2** Term 2 means this . . .
**term 3** Term 3 means this . . .

In that example, "Glossary" is the header, and the three lines after it are glossary items. The bolded words are glossary terms.

This MR also includes a re-arrangement of the class definitions for the groups within tabs in the production editor; having more than one class in a tag makes eslint unhappy.

Here's what the UI looks like: