Simplify startup and improve its animation

- Remove Python.loadingAccounts/willLoadAccounts
- Fix HPage SwipeView bug that caused its inner SidePane to steal focus

- Use overshoot for animation
- Get rid of sidepane flickering
- Set default HNumberAnimation easing.type to OutQuad, specify InOutQuad
  for HCheckBox

src/qml/Window.qml

@@ -43,6 +43,6 @@ ApplicationWindow {
         scale: py.ready ? 1 : 0.5
         source: py.ready ? "UI.qml" : ""
 
-        Behavior on scale { HNumberAnimation {} }
+        Behavior on scale { HNumberAnimation { overshoot: 5; factor: 1.2 } }
     }
 }