Kivy: Add a button prompt box (#3470)

* Kivy: Add a button prompt box

* auto format the buttons to display 2 per row to look nicer

* update to kivymd

* have the uri popup use the new API

* have messenger use the new API

* make the buttonprompt import even more lazy

* messenger needs to be lazy too

* make the buttons take up the full dialog width

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Co-authored-by: NewSoupVi <57900059+NewSoupVi@users.noreply.github.com>

data/client.kv

@@ -222,3 +222,8 @@
         spacing: 10
         size_hint_y: None
         height: self.minimum_height
+<MessageBoxLabel>:
+    valign: "middle"
+    halign: "center"
+    text_size: self.width, None
+    height: self.texture_size[1]