Disable animations for flashing red window on timer expiration

[HDkarlsen]

Suggestion: add an option to disable the red flashing animation of the expired timer. As mentioned in issue #156, this causes some users (me included) to have the GPU go crazy. I assume it's the flashing that does it. If the expired timer could turn red without any animations, perhaps we could use Hourglass without fearing that the fan will cause the computer to fly off. You mentioned in that issue that it was hard for you to work on it without a machine with Nvidia mobile GPU. I use your app daily, and love its simplicity. Would be fantastic to have this one bug eliminated.