Name things like set_outgroup when that is what they are doing.

We had a legacy name for the gui communication, where "root_at" really
meant "set_outgroup". To "root at a node" means something different,
and we might want to use that independently. This change makes it all
cleaner.

ete4/smartview/gui/server.py

@@ -510,7 +510,7 @@ def callback(tree_id):
     sort(tree_id, node_id, key_text, reverse)
     return {'message': 'ok'}
 
-@put('/trees/<tree_id>/root_at')
+@put('/trees/<tree_id>/set_outgroup')
 def callback(tree_id):
     tree_data, subtree = touch_and_get(tree_id)
 

ete4/smartview/gui/static/js/contextmenu.js

@@ -295,11 +295,11 @@ async function add_node_modifying_options(properties, nodestyle, node_id) {
     }, "Edit the content of this node. Changes the tree structure.",
        "edit", true);
     if (!view.subtree) {
-        add_button("Root on this node", async () => {
-            await tree_command("root_at", node_id);
+        add_button("Set node as outgroup", async () => {
+            await tree_command("set_outgroup", node_id);
             draw_minimap();
             update();
-        }, "Set this node as the root of the tree. Changes the tree structure.",
+        }, "Set this node as the 1st child of the root. Changes the tree structure.",
            "root", true);
     }
     add_button("Move branch up", async () => {

ete4/smartview/gui/static/js/gui.js

@@ -294,7 +294,7 @@ async function tree_command(command, params=undefined) {
     try {
         await api_put(`/trees/${get_tid()}/${command}`, params);
 
-        const commands_modifying_size = ["root_at", "remove", "update_props"];
+        const commands_modifying_size = ["set_outgroup", "remove", "update_props"];
         if (commands_modifying_size.includes(command))
             view.tree_size = await api(`/trees/${get_tid()}/size`);
     }