Add xorg window manager detection with xprop

[Gobidev]

Add another way of optaining the window manager name on Xorg using xprop.
This method works on most systems and uses a pre-installed command. If the detection with xprop fails, the previous method of using wmctrl will be tested and errors will only be returned if this also fails.

[grtcdr]

Although I'd love to see a Rust-native implementation so we can finally close #9, this is a welcome change, so thank you!

[Gobidev]

The only Rust-native implementation I can think of would be to scan /proc for known WMs, which would also work for wayland but could not detect WMs that are not hardcoded. However, we could then fallback to using xprop and/or wmctrl, maybe I will look into that in the future.