refactor Version.Manager and .Provider into own classes

This patch does:
 * refactor the Manager and Provider into separate classes in the
   hierarchy, comparable to iqprivate
 * update extensions.provider
 * rework how START_TAG parsing is done
 * re-use of the NAMESPACE element
 * removal of flood protection
 * weak-reference connection class
 * improve packet filter in the manager
 * add a test case