matrix-org#2220)

Set the limit on the returned events in the timeline in the get and sync
operations. The default value is -1, means no upper limit.

For example, using `filter_timeline_limit: 5000`:

POST /_matrix/client/r0/user/user:id/filter
{
room: {
    timeline: {
      limit: 1000000000000000000
    }
}
}

GET /_matrix/client/r0/user/user:id/filter/filter:id

{
room: {
    timeline: {
      limit: 5000
    }
}
}

The server cuts down the room.timeline.limit.

* Added HS as property in SyncRestServlet
* Fixed set_timeline_upper_limit function implementat¡ion