add support for arbitrary refresh rates in the select animation

[SaphiraKai]

This is almost entirely copy-pasted from its sister PR for instantWM. It uses XRandR to detect the display's native refresh rate and render the selection animation accordingly.

[SaphiraKai]

Ugh... Apparently usleep() is deprecated in favor of nanosleep(). I was about to go make a PR to migrate to it, but apparently nanosleep() takes a stupid timespec struct as an argument instead of just a number... Because obviously making things more complicated for no reason makes perfect sense

Do you think we could just hit the ignore button on that check issue?