Monitor detection cache issues

[DarNCelsius]

This is probably related to my earlier comment in the last issue #73 where the display was not detected.

Here's today's output:

I don't think reading from cache is useful when detecting monitors...

[LinusDierheimer]

I implemented caching for resolution, because in a typical workflow monitors aren't changed too often and detection was time expensive. In the current state however, i managed to get some decent performance (especially since XWayland is never used), so i will remove caching for it in the next commit.