Kill the actions UI. With fire.

☺

Remove ActionManager from a bunch of plugins.

Move StringTransferable to components.

Use the new comparator for modes in the nicklist.

I think all that's left is the actions UI itself, and the perform
stuff.

Use new unread status events.

Implement mode comparator for ClientInfo.

Tidy WindowStatusManager.

Fix Contactlist plugin after recent changes.

Make more things use GroupChatUser.

  - Also by AutoValue Topic
  - Also make getUser in Topic Optional

Fixups for away colours plugin.

Use GroupChatUser some more.

Minor DCC tidying.

Fix some nullable annotations in debug plugin.

Remove TopicChangeListener. Add Topic to topic events.

Fixes for latest GroupChatUser changes.

Tidy up NickList + Renderer.

Convert ContactListListener to events.

Fix remaining null-passing method.

Stop the XMPP parser passing null to callbacks.

Don't use addNonCriticalCallback.

All this does is suppress a runtime exception that should never
occur in these cases.

If a callback isn't found then it's a serious error and should
be handled properly, not squelshed.

Fix XMPP parser for latest parser changes.