[IMP]tree row click to switch to form view default

Original **tree view** row double click default behavior is to  send a `/web/treeview/action` rpc returns empty, and the web page is nothing changed.
Modify the **tree view** row double click default behavior : try to switch to **form** view.
Make the default behavior is just like the **list view** does.

If the `tree_but_open` ir_value is set, the default behavior will not be executed, the `tree_but_open` will instead it.

btw. I try to config the `tree_but_open` to open a specific record form for about 2 hours, but failed. I don't know is that an issue?