Prior to this fix, Smack requires the 'open' element send on a websocket connection to be collapsed. With the change in
this commit, an expanded (eg: `<open ...></open>`) element can also be used.
fixes SMACK-935
This also lifts a bunch of logic from smack-websocket-okhttp into
smack-websocket. Furthermore, the following subprojects require now
Java 11:
- smack-integration-test
- smack-omemo-signal-integration-test
- smack-repl
- smack-websocket-java11
Related tracking issue: SMACK-835