Focus the proposal selection switch after pressing it

Since this button is replaced by a new element in an AJAX call, nothing
was focused after pressing it.

So we're reusing the code we used to enable/disable budget phases, which
already dealt with this issue.

app/views/admin/shared/_toggle_switch.js.erb

@@ -0,0 +1,5 @@
+var new_toggle_switch = $("<%= j new_content %>");
+var current_toggle_switch = $("#<%= dom_id(record) %> .toggle-switch");
+
+current_toggle_switch.replaceWith(new_toggle_switch);
+new_toggle_switch.find("[type='submit']").focus();