refactor: clean up some MainWindow stuff

this makes the accounts button and menubar item share the same QMenu
and also refactors some code

Signed-off-by: leo78913 <leo3758@riseup.net>

launcher/ui/MainWindow.ui

@@ -487,6 +487,9 @@
    </property>
   </action>
   <action name="actionNoDefaultAccount">
+   <property name="checkable">
+    <bool>true</bool>
+   </property>
    <property name="icon">
     <iconset theme="noaccount">
      <normaloff>.</normaloff>.</iconset>
@@ -494,6 +497,9 @@
    <property name="text">
     <string>No Default Account</string>
    </property>
+   <property name="shortcut">
+    <string>Ctrl+0</string>
+   </property>
   </action>
   <action name="actionCloseWindow">
    <property name="icon">