Renamed reference in user interface text and set sidebar position

Author: HLeithner

docs/user-interface-text/zreferences.md renamed to docs/user-interface-text/references.md

@@ -1,4 +1,9 @@
+---
+sidebar_position: 999
+---
+
 # External References
+
 ## Main en-GB Sources
 * [gov.uk](https://www.gov.uk/guidance/style-guide/a-to-z-of-gov-uk-style) [(licence)](https://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/)
 * [The BBC](https://www.bbc.co.uk/newsstyleguide/all/)