Implement global schedule widget for all conference events

[MurzNN]

Is your feature request related to a problem? Please describe.
Now we already have per-room schedule widgets, that shows list of events. But when conference member attends in events from multiple rooms, it's very inconvenient to always switch between rooms to check schedule in some other room.

Describe the solution you'd like
Good solution can be implementing the widget with global schedule from all rooms, with links to quick jump into event's room on each item. And attach this event to main room of conference (lobby or other).

Additionally will be good to have user filter to show-hide rooms, add to bookmarks (with storing items in room's account_data) and other cool features, for example DM room with bot which will remind you on bookmarked event start.

Describe alternatives you've considered
Alternative is to use mobile app as companion to desktop, but we can't quickly switch from mobile app to desktop's room.
Other alternative is to use website with same functionality, but have all the needs inside Matrix client is more convenient!