UID2 minor edits

[genwhittTTD]

To match mods made in EUID PR #406 and also a few extras in EUID PR #411.

• Removing UID2 prefix from some document titles -- not necessary given the context
• v2 identity map > POST /v2/identity/map (in headings and links to it). Same for v3.
• Made sure all instances of Private Operator and Public Operator are consistently initcap (fixed a couple).
• Fixed one error where a link was pointing to the current version rather than the old one.