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.
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