Currently the viewer frame on Windows and Linux have an ugly platform-specific header with a title, close buttons, and a minimize button.

We should just replace those with our own window frame, like in https://github.com/emilk/egui/tree/master/examples/custom_window_frame

TODO:

• Fix window resizing UI on Wayland and Xorg
• Fix lower right corner (paint_time_ranges_gaps). Maybe turn off rounding?
• Test on Windows
• Custom icons for close/maximize/minimize
• I think we need to center the panel buttons?

What Rerun currently looks like on Gnome/xorg:

If you enable CUSTOM_WINDOW_DECORATIONS on main: