Room screen: timeline message bubbles (#91)

* #34 Create `TimelineItemStylerView`

* #34 Add styler view into different type of cells

* #34 Use placeholder avatar image on room list

* #34 Add `isOutgoing` param to event based timeline item

* #34 Compute `isOutgoing` for timeline items

* #34 Update sender info view in timeline

* #34 Update mock timeline items

* #34 Rename `EventBasedTimelineView` to `EventBasedTimelineSenderView`

* #34 Change padding on timeline cells

* #34 Create `TimelineItemStylerView` to move content into a bubble if needed

* #34 Use styler view in all of the timeline item views

* #34 Make timestamp more readable on images

* #34 Little layout tweaks

* #34 Add changelog

* #34 Fix code smells

* #34 Set text colors on timeline items

* #34 Fix background color of the timeline

* #34 Fix PR remarks

* #34 Set background colors explicitly on remaining screens

* #34 Reduce min bubble width and make it a scaled metric

* #34 Refactor `PlaceholderAvatarImage` to accept a text only

* #34 Fix code smell

* #34 Fix further comments

ElementX/Sources/Screens/RoomScreen/View/RoomHeaderView.swift

@@ -45,7 +45,7 @@ struct RoomHeaderView: View {
                 .scaledToFill()
                 .accessibilityIdentifier("roomAvatarImage")
         } else {
-            PlaceholderAvatarImage(firstCharacter: String(context.viewState.roomTitle.first ?? Character("")))
+            PlaceholderAvatarImage(text: context.viewState.roomTitle)
                 .accessibilityIdentifier("roomAvatarPlaceholderImage")
         }
     }
@@ -78,7 +78,7 @@ struct RoomHeaderView_Previews: PreviewProvider {
         let viewModel = RoomScreenViewModel(timelineController: MockRoomTimelineController(),
                                             timelineViewFactory: RoomTimelineViewFactory(),
                                             roomName: "Some Room name",
-                                            roomAvatar: Asset.Images.appLogo.image,
+                                            roomAvatar: nil,
                                             roomEncryptionBadge: Asset.Images.encryptionTrusted.image
         )