Final Expressions

[JPryce-Aklundh]

This PR does the following:

• Removes the old Expressions overview page (outdated).
• Creates 2 new pages from its obliteration (values-and-types/numeric-string-boolean.adoc and values-and-types/graph-references)
• Redirects any remaining links to the old Syntax/operators page (gone) and Expressions overview page

[neo4j-docops-agent]

Thanks for the documentation updates.

The preview documentation has now been torn down - reopening this PR will republish it.