Bring back the numbers in the "Move To Desktop" menu

They were removed by commit 0bd65de3 because they seemed redundant in "Move to 1 Desktop 1", but

• that was just wrong ordering, should have been "1 Move to Desktop 1"
• the number at the front is used as accelerator for fast keyboard usage
• not everyone keeps numbers in their desktop names

=> reintroduce numbers, but at the front and in parenthesis, like "(1) Move to Desktop 1" (wayland) or "(1) Desktop 1" (X11)

Used a simple counter starting from 1 rather than the x11DesktopNumber() value which was called "legacyID" in the code.