Bump version to 4.7.0

[pfefferle]

Summary

Prepare the 4.7.0 release:

• Bump the plugin version to 4.7.0 in indieauth.php and the stable tag in readme.md
• Sync INDIEAUTH_PLUGIN_VERSION, which was still set to 4.5.5 (missed in the 4.6.0 bump)
• Add the 4.7.0 changelog entries
• Fix PHP 7.4 compatibility: the nullsafe operator (?->) introduced in Call function instead of the global variable #317 is PHP 8.0 syntax and causes a parse error on PHP 7.4. Assign a local $current_user from wp_get_current_user() instead, which also fixes the remaining usages of the unset global in the template.

Changelog

• Fix fatal error on the authorization form when the current user cannot be determined (Fix fatal error from undefined function __e() #314)
• Fix user detection on the authorization form by calling wp_get_current_user() instead of relying on the global variable (Call function instead of the global variable #317)
• Modernize codebase with namespaces, an autoloader and a new folder structure (Modernize codebase: namespaces, autoloader, folder structure #306)

Release steps

After merging, tag trunk as 4.7.0 and push the tag — the deploy workflow will publish to WordPress.org.