resip/stack: WebSockets: use standalone class for parsing, code optimization

git-svn-id: https://svn.resiprocate.org/rep/resiprocate/main@10171 ddefafc4-47db-0310-ae44-fa13212b10f2
-allow AllowEvents to be an advertised capability

git-svn-id: https://svn.resiprocate.org/rep/resiprocate/main@10172 ddefafc4-47db-0310-ae44-fa13212b10f2