This change is with an eye on supporting reserved nicknames, in which case the
user who has a reserved nickname won't have to choose a nick upon joining a
room.

because we don't always have a jid...

You can now provide the JID of the server either via `converse.initialize` or
via `converse.user.login`.

before converse.initialize has been called. Otherwise we won't get
translations.

Updates #669

Also add an initial test case for filtering by chat state.

and don't remove during `_tearDown`.

Fixes bug in `trimChats` when logging in again and `converse.minimized_chats`
is undefined.

Fixes bug when fetching controlbox, which doesn't have a jid

Use the 128x128 icon for Desktop notifications

due for example to it being called by an event handler.

to ensure naming consistency, we have the same method on `ChatRoomView`.

Move init of RosterGroups collection and presenceHandler registration out of
the controlbox and rosterview plugins and into core, since this code is
generally useful (indeed necessary) even without those plugins.

In some cases the element is not visible,but we want to set 'display: None'
regardless, for example in cases where you only want one single chat of
multiple to be visible at any one time, while hiding it behind a sidebar.

to indicate whether the room should be created if not found.

By listening for this event before registering event handlers, other plugins
can first get their overrides of those handlers applied.