Draft: system: Create subpages when idle to speed up startup
By starting the System panel with all its pages we end up constructing each of them. Some of the pages establish sync DBus connections when created and those combined can make the System panel startup noticibly slow.
Let's use g_idle_once to add the subpages after the main System panel has been created.
See #2857 (closed)
These are a couple of optimizations that I guess could help here. I want to follow up on this by doing proper measuring, using sysprof.