1. enable avatars in autocomplete
2. change search/filter type for automcomplete

Fixes #1769

- Move headless one-on-one chat functionality into converse-chat
- Split converse-headline into converse-headlines and converse-headlines-views
- Add api in `_converse.api.chatboxes` for creating chatboxes
- Add `_converse.api.controlbox.get` method

will add for more

Instead of taking an integer for the `type`, "info", "warn" or "error" should be passed in.

VCards were being created before `fetch` was completed, so once fetch
was done those VCards were unset from their collection.

Add a new event and promise `VCardsInitialized` that triggers after
successful fetching and wait for it before creating VCards.

Depend on latest backbone.browserStorage which has support for IndexedDB
via localforage.

Storage operations are now asynchronous and transactional.

Bugs fixed (mostly by waiting for operations to complete):

* Rooms are now fetched asynchronously, so wait before triggering `show`
  or when closing.
* Make sure chat create/update transactions complete before firing events
* Make sure chats and messages have been fetched before creating new ones.
* When doing a `fetch` with `wait: false` on a collection and then
  creating a model in that collection, then once the read
  operation finishes (after creating the model), the collection is emptied again.
* Patch and wait when saving.
  Otherwise we have previously set attributes overriding later ones.
* Make sure api.roomviews.close returns a promise

Test fixes:

* Chats are now asynchronously returned, so we need to use `await`
* Wait for the storage transaction to complete when creating and updating messages
* Wait for all chatboxes to close
    Otherwise we get sessionStorage inconsistencies due to the async nature of localforage.
* Wait for room views to close in spec/chatroom.js

In the process, remove the `closeAllChatBoxes` override in
converse-controlbox by letting the `close` method decide whether it
should be closed or not.

- Increase z-index for chatbox flyouts so that they appear above the controlbox
- Also fix a margin offset bug for the controlbox (in smaller viewports)

Also move some other methods out of `converse-core` into the plugins
that use them.

- Always try to first get local cache before requesting the roster.
- Rename `roster_fetched` with `roster_cached`

Doesn't appear to be very useful. IIRC it was added as a workaround for
slow roster issues.

This was used for tests but is no longer necessary.

- Inform the user when fetching of bookmarks times out.
- Only set the cached flag if the user doesn't have bookmarks.

This is in anticipation of the localforage/IndexDB merge