plugin XEP-0048, XEP-0402; CLI (bookmarks): implement XEP-0402 (PEP Native Bookmarks): - Former bookmarks implementation is now labeled as "legacy". - XEP-0402 is now used for bookmarks when relevant namespaces are found, and it fallbacks to legacy XEP-0048/XEP-0049 bookmarks otherwise. - CLI legacy bookmark commands have been moved to `bookmarks legacy` - CLI bookmarks commands now use the new XEP-0402 (with fallback to legacy one automatically used if necessary).