In order to resolve the conflict between local and remote read-receipts, try to
give precedence to the read-receipt which refers to the most recent event.
Also fix the read-receipt synthesis in _addLiveEvents so that it actually works
(drop the spurious MatrixEvent wrapper), and remove the synthesis in
recalculate() (which appears to be redundant).
This provides optional support for fetching old events via the /context API,
and paginating backwards and forwards from them, eventually merging into the
live timeline.
To support it, events are now stored in an EventTimeline, rather than directly
in an array in the Room; the old names are maintained as references for
compatibility.
The feature has to be enabled explicitly, otherwise it would be impossible for
existing clients to back-paginate to the old events after a gappy /sync.
Still TODO here:
* An object which provides a window into the timelines to make them possible to
use. This will be a separate PR.
* Rewrite the 'EventContext' used by the searchRoomEvents API in terms of an
EventTimeline - it is essentially a subset.
Add polyfills for Array.map/filter according to MDN because it looks much
better than the utils format.
Add stub tests for edge cases and implement test for the common case.
This makes it easier to localise in the future (if name == '?'), whilst
still indicating an unknown name. Ideally we would be returning null, but
this would require null checks every time the room name was accessed, which
isn't ideal. This also makes the UT for this less brittle (rather than
comparing literal english strings which are prone to breakage when we
inevitably change 'Unknown' to 'unknown' or something else.
