A way to add context to references

[jkomoros]

References have an ability to have text in them. By default everything but type link has an empty ''. But for some reference types it could encode useful information.

For example, a citation-person reference with non-empty text might encode the URL of a work, that doesn't make sense to factor out into a card. Or a citation to a work might include a pg 437.

This shouldn't be THAT hard to integrate.

Useful for #465

• Add an ability to pass a value in EDITING_ADD_REFERENCE
• Make sure that the reference diffing machinery will allow adding a text tag
• Make it so clicking on a tag in editor will pop a prompt to add/remove text.
• Make it so tags in editor that have extra text show a little info icon and on hover show the extra text.
• Make it so there's some way to view the text--ideally in the card-info-panel for non-empty ones. (Does this require some bigger project to pass through some sortExtras kind of thing?)
• The prompt to ask for a value should show different text for different reference types with suggested use
• some kind of convention or checking for different types, a referenceTextValdiator. For example for citation it might validate that it is a comma-delimited list of page <number>.