Canonical Parent

So the original space parent and child stuff was technically a bit naughty in that it allowed multiple rooms to be set as the canonical parent. Because while a room can have multiple parents only one should be canonical. This adds the following:
- When adding a child or parent there is an extra check to select if the new parent should be canonical
- Any parent can be selected as the canonical one from the room settings
- All functions ensure that there is only ever one canonical parent by ensuring all others are false when a new one is set.

src/qml/SpaceHomePage.qml

@@ -157,12 +157,12 @@ Kirigami.Page {
             }, {
                 title: i18nc("@title", "Create a Child")
             })
-            dialog.addChild.connect((childId, setChildParent) => {
+            dialog.addChild.connect((childId, setChildParent, canonical) => {
                 // We have to get a room object from the connection as we may not
                 // be adding to the top level parent.
                 let parent = root.currentRoom.connection.room(parentId)
                 if (parent) {
-                    parent.addChild(childId, setChildParent)
+                    parent.addChild(childId, setChildParent, canonical)
                 }
             })
             dialog.newChild.connect(childName => {spaceChildrenModel.addPendingChild(childName)})