Update version+variant menu, add siteGetPage shortcode, add tdVersion struct, and more

[chalin]

• Updates and uifies version+variant menus for all three config profiles
• Defines a new tdVersion YAML struct to hold version metadata (latest, dev, buildId) with YAML anchors
• Refactors set-package-version scripts to support the new tdVersion YAML group
• Adds siteGetPage for use in test pages
• Some doc updates
• Note that version v-prefix use has changed: the old config used bare versions like 0.14.4-dev; the new config consistently uses v-prefixed versions like v0.14.4-dev.