[jitsi-dev] Update to Smack 4.2


As discussed in The Call yesterday, I've created pull requests for the Jitsi
Meet components to update them to Smack 4.2. Since the projects all depend
on one another, the PR tests are failing. If you want to test locally, you
need to "mvn install" the projects in the following order:

- jnsapi (branch jitsi-smack-4-2)
- jitsi
- jicoco (https://github.com/jitsi/jicoco/pull/28)
- videobridge (https://github.com/jitsi/jitsi-videobridge/pull/528)
- jicofo (https://github.com/jitsi/jicofo/pull/217)
- jigasi (https://github.com/jitsi/jigasi/pull/82)
- jitsi-hammer (https://github.com/jitsi/jitsi-hammer/pull/26)

Please also comment on the PRs if you find anything without actually running
the projects. I know that the PRs are large and hard to just look at, but
smaller just isn't possible :frowning: