I think this was responsible for the readmarker just disappearing rather than
animating.
While we're here, decrease the delay on the animation, and instead make it take
slightly longer to disappear.
This fixes an issue where the RM appeared before any events which were pending
when you switched away from that room
(https://github.com/vector-im/vector-web/issues/1241).
Also, fix a buglet in the MessagePanel which meant we didn't animate the
disappearance of a RM when it stayed at the same event but became
invisible. This didn't really cause any user-visible problems (because
typically we advance the RM at the same time as it became invisible), but
confused me a bit while I was trying to debug this.
Rather than telling react-gemini-scrollbar to update every time something that
changes its size happens, try out our fork of it which uses some hackery to
listen for resizes.
We need two modes of operation for ScrollPanel.scrollToToken:
For jump-to-read-marker, we want it 1/3 of the way down the screen.
For search clickthrough, and hyperlinked events, we want put the event in the
*middle* of the screen.
Fixes https://github.com/vector-im/vector-web/issues/1032
Make the onImageLoad handler call checkScroll on the right thing. This was
originally done in commit 99d2392, but got broken in the Great RoomView
Refactor of February 2016.
