Rework how messages and events are handled

- No more translatable, content_type, show_name_line attrs for
  TimelineEventReceived.
  Since they are UI concerns, they are handled directly in QML.

- Refactor the EventDelegate and get rid of errors when new items
  are added to the timeline

- Messages, events and emotes all combine correctly.

- No more 28px wide avatars for events, to make them uniform with
  messages.

src/qml/Chat/Timeline/EventList.qml

@@ -4,6 +4,7 @@
 import QtQuick 2.12
 import SortFilterProxyModel 0.2
 import "../../Base"
+import "../../utils.js" as Utils
 
 HRectangle {
     property alias listView: eventList
@@ -14,6 +15,37 @@ HRectangle {
         id: eventList
         clip: true
 
+        function canCombine(item, itemAfter) {
+            if (! item || ! itemAfter) { return false }
+
+            return Boolean(
+                ! canTalkBreak(item, itemAfter) &&
+                ! canDayBreak(item, itemAfter) &&
+                item.senderId === itemAfter.senderId &&
+                Utils.minutesBetween(item.date, itemAfter.date) <= 5
+            )
+        }
+
+        function canTalkBreak(item, itemAfter) {
+            if (! item || ! itemAfter) { return false }
+
+            return Boolean(
+                ! canDayBreak(item, itemAfter) &&
+                Utils.minutesBetween(item.date, itemAfter.date) >= 20
+            )
+        }
+
+        function canDayBreak(item, itemAfter) {
+            if (! item || ! itemAfter || ! item.date || ! itemAfter.date) {
+                return false
+            }
+
+            return Boolean(
+                itemAfter.eventType == "RoomCreateEvent" ||
+                item.date.getDate() != itemAfter.date.getDate()
+            )
+        }
+
         model: HListModel {
             sourceModel: timelines