App polish part 2 (#1118)

- Fix sheet backgrounds in dark mode.
- Fix background colours for reaction buttons.
- Reply view layout.
- Update separator colours.
- Don't show sender name/avatar in DMs.
- Fix inconsistent line heights with formatted body text.
- Use plain text for reply
- Increase tappable size of collapsed state changes button.
- Blockquote layout and text colour.
- Tap to expand the topic in room details.
- Change the topic and security font size in room details.
- Add cancel button when inviting someone to an existing room.
- Reword Add Friends to Add People in start chat screen.
- Update compound.

ElementX/Sources/Screens/InviteUsersScreen/InviteUsersScreenViewModel.swift

@@ -51,6 +51,8 @@ class InviteUsersScreenViewModel: InviteUsersScreenViewModelType, InviteUsersScr
     
     override func process(viewAction: InviteUsersScreenViewAction) {
         switch viewAction {
+        case .cancel:
+            actionsSubject.send(.cancel)
         case .proceed:
             switch roomType {
             case .draft: