Add RoomList.local_unread_markers option to settings.py,
which is False by default.
Before, this way always enabled and conflicts with push rules by marking
anything as unread without any logic.
- Notifications.alert_time → Notifications.flash_time,
more evocative of what these "alerts" actually do
- Change default for the above from 0 to 5, since now push rules already
control precisely what to enable or disable these alerts for
- Notifications.urgent_alert_time → Notifications.highlight_flash_time,
"highlight" is the term used in the matrix doc
When messages are selected in the timeline, change the chat header's
mode to show how many messages are selected and offer copy, remove and
deselect buttons.
