Add the empty state to SpaceScreen. (#4985)

* Rename PaginationState.timelineEndReached to PaginationState.endReached.

* Rename PaginationState to TimelinePaginationState.

Also renames PaginationStatus to PaginationState so that a TimelinePaginationState consists of the forward and backward pagination states.

* Add the empty state to SpaceScreen.

Only has 1 of the 2 buttons for now.

ElementX/Sources/Screens/Timeline/TimelineModels.swift

@@ -210,7 +210,7 @@ struct RoomMemberState {
 /// Is also nice to have this as a wrapper for any state that is directly connected to the timeline.
 struct TimelineState {
     var isLive = true
-    var paginationState = PaginationState.initial
+    var paginationState = TimelinePaginationState.initial
     
     /// The room is in the process of loading items from a new timeline (switching to/from a detached timeline).
     var isSwitchingTimelines = false

ElementX/Sources/Screens/Timeline/TimelineTableViewController.swift

@@ -109,7 +109,7 @@ class TimelineTableViewController: UIViewController {
     }
     
     /// The state of pagination (in both directions) of the current timeline.
-    var paginationState: PaginationState = .initial {
+    var paginationState: TimelinePaginationState = .initial {
         didSet {
             // Paginate again if the threshold hasn't been satisfied.
             paginatePublisher.send(())

ElementX/Sources/Screens/Timeline/TimelineViewModel.swift

@@ -614,7 +614,7 @@ class TimelineViewModel: TimelineViewModelType, TimelineViewModelProtocol {
                 break
             }
             
-            if state.timelineState.paginationState.forward == .timelineEndReached {
+            if state.timelineState.paginationState.forward == .endReached {
                 focusLive()
             }