ui: use custom button

pqcli/ui/button.py

@@ -0,0 +1,11 @@
+import urwid
+
+
+class MenuButton(urwid.Button):
+    def __init__(self, label, *args, **kwargs):
+        super().__init__("", *args, **kwargs)
+        self._w = urwid.AttrMap(
+            urwid.SelectableIcon(["\N{BULLET} ", label], 2),
+            "button",
+            "button-focus",
+        )