Detect the Vimium Chrome extension

Detect whether the Vimium Chrome extension is installed. Tested on Vimium v1.59. As for an official solution to Vimium detection, keep an eye on Vimium issue#2399

hasVimium returns true if Vimium is detected, false otherwise. This detection is not 100% accurate.

if(hasVimium()){alert("Hey, you have Vimium!");}else{alert("I don't detect Vimium, but it might still be there.");}