Hide avatar of inviting user when images are hidden by default

While this reuses the setting for a slightly different purpose, in practice, these safety feature really belong together and it makes sense to have them both under a single option.
In the future, we might want to rephrase the options description

src/app/qml/InvitationView.qml

@@ -33,7 +33,7 @@ ColumnLayout {
         Layout.fillWidth: true
 
         name: root.invitingMember.displayName
-        source: root.invitingMember.avatarUrl
+        source: NeoChatConfig.hideImages ? undefined : root.invitingMember.avatarUrl
         color: root.invitingMember.color
     }