Remove all Backend "get_any_client"-using methods

thumbnail() and download() were remaining.
Use a direct and carefully chosen MatrixClient's methods instead to
avoid problems mentioned in the previous commit 7502c1.

src/gui/Pages/AccountSettings/Account.qml

@@ -93,6 +93,7 @@ HFlickableColumnPage {
 
         property bool changed: Boolean(sourceOverride)
 
+        clientUserId: page.userId
         userId: page.userId
         displayName: nameField.item.text
         mxc: account ? account.avatar_url : ""

src/gui/Pages/AddChat/CreateRoom.qml

@@ -69,6 +69,7 @@ HFlickableColumnPage {
 
     HRoomAvatar {
         id: avatar
+        clientUserId: page.userId
         roomId: ""
         displayName: nameField.item.text
 

src/gui/Pages/AddChat/CurrentUserAvatar.qml

@@ -8,7 +8,7 @@ HUserAvatar {
     property QtObject account
 
 
-    // userId: (set me)
+    clientUserId: userId
     displayName: account ? account.display_name : ""
     mxc: account ? account.avatar_url : ""
 

src/gui/Pages/Chat/AutoCompletion/CompletableUserDelegate.qml

@@ -16,6 +16,7 @@ HTile {
 
         HUserAvatar {
             id: avatar
+            clientUserId: chat.userId
             userId: model.id
             displayName: model.display_name
             mxc: model.avatar_url

src/gui/Pages/Chat/Banners/Banner.qml

@@ -40,6 +40,7 @@ Rectangle {
 
                 HUserAvatar {
                     id: bannerAvatar
+                    clientUserId: chat.userId
                     anchors.centerIn: parent
                     radius: 0
                 }

src/gui/Pages/Chat/Composer/Composer.qml

@@ -25,6 +25,7 @@ Rectangle {
         HUserAvatar {
             id: avatar
             radius: 0
+            clientUserId: messageArea.writingUserId
             userId: messageArea.writingUserId
 
             mxc:

src/gui/Pages/Chat/RoomHeader.qml

@@ -52,6 +52,7 @@ Rectangle {
 
         HRoomAvatar {
             id: avatar
+            clientUserId: chat.userId
             roomId: chat.roomId
             displayName: chat.roomInfo.display_name
             mxc: chat.roomInfo.avatar_url

src/gui/Pages/Chat/RoomPane/MemberView/MemberDelegate.qml

@@ -23,6 +23,7 @@ HTile {
 
         HUserAvatar {
             id: avatar
+            clientUserId: chat.userId
             userId: model.id
             displayName: model.display_name
             mxc: model.avatar_url

src/gui/Pages/Chat/RoomPane/MemberView/MemberProfile.qml

@@ -61,6 +61,7 @@ HListView {
             root.currentIndex = 0
 
         HUserAvatar {
+            clientUserId: chat.userId
             userId: member.id
             displayName: member.display_name
             mxc: member.avatar_url

src/gui/Pages/Chat/RoomPane/SettingsView.qml

@@ -82,6 +82,7 @@ HFlickableColumnPage {
 
     HRoomAvatar {
         id: avatar
+        clientUserId: chat.userId
         roomId: chat.roomId
         displayName: nameField.item.text || chat.roomInfo.display_name
         mxc: chat.roomInfo.avatar_url

src/gui/Pages/Chat/Timeline/EventContent.qml

@@ -94,6 +94,7 @@ HRowLayout {
 
         HUserAvatar {
             id: avatar
+            clientUserId: chat.userId
             userId: model.sender_id
             displayName: model.sender_name
             mxc: model.sender_avatar

src/gui/Pages/Chat/Timeline/EventImage.qml

@@ -60,6 +60,7 @@ HMxcImage {
     height: fitSize.height
     horizontalAlignment: Image.AlignLeft
 
+    clientUserId: chat.userId
     title: thumbnail ? loader.thumbnailTitle : loader.title
     animated: eventList.isAnimated(loader.singleMediaInfo)
     thumbnail: ! animated && loader.thumbnailMxc

src/gui/Pages/Chat/Timeline/EventList.qml

@@ -416,6 +416,7 @@ Rectangle {
             window.makePopup(
                 "Popups/ImageViewerPopup/ImageViewerPopup.qml",
                 {
+                    clientUserId: chat.userId,
                     thumbnailTitle: getThumbnailTitle(event),
                     thumbnailMxc: event.thumbnail_url,
                     thumbnailPath: eventList.thumbnailCachedPaths[event.id],
@@ -459,6 +460,7 @@ Rectangle {
             print("Downloading " + event.media_url + " ...")
 
             const args = [
+                chat.userId,
                 event.media_url,
                 event.media_title,
                 JSON.parse(event.media_crypt_dict),