Summary:
Change the three dotted menu to use PlasmaComponents ContextMenu.
This prevents menu from staying open on other system tray's applets.
Wayland still has that issue, happens in other menus too.
BUG: 415142

And change menu icon into a hamburger menu.

Test Plan:
Before:
Open the menu, and then open an other applet. Menu will stay open on
the left. Even if change windows and open the system tray, will still
be there.
After:
Use X11. By clicking, for example volume applet, menu will minimize.
Will need to click again to open the applet.