Add an obvious "upload" button in the account editor

It's not obvious at first glance that you can click on the avatar in the
account editor to upload an image. This adds a new button when there is
no image uploaded.

src/qml/Settings/AccountEditorPage.qml

@@ -62,6 +62,23 @@ Kirigami.ScrollablePage {
                 fileDialog.open();
             }
 
+            QQC2.Button {
+                anchors {
+                    bottom: parent.bottom
+                    right: parent.right
+                }
+                visible: avatar.source.toString().length === 0
+                icon.name: "cloud-upload"
+                text: i18n("Upload new avatar")
+                display: QQC2.AbstractButton.IconOnly
+
+                onClicked: parent.onClicked()
+
+                QQC2.ToolTip.text: text
+                QQC2.ToolTip.visible: hovered
+                QQC2.ToolTip.delay: Kirigami.Units.toolTipDelay
+            }
+
             QQC2.Button {
                 anchors {
                     bottom: parent.bottom