aw-qt long start/exit

When you start aw-qt it takes like 20 seconds to start up before it's usable.
Also after I press `Quit ActivityWatch` button in the right-click menu it takes like 20 seconds for the confirmation dialog to show up.

I think both of those are related to outdated fontconfig as I've seen similar reports for other programs ([telegram](https://github.com/telegramdesktop/tdesktop/issues/4240), [peek](https://forum.snapcraft.io/t/arch-linux-some-snaps-take-a-long-time-to-show-a-gui/4844/2), [chromium](https://bugs.chromium.org/p/chromium/issues/detail?id=829890&can=2&q=fontconfig))

This https://github.com/ActivityWatch/aw-qt/issues/33 should probably solve it, but I think it's better for it to be saved here to make sure it's fixed later.

Arch linux, AW installed via AUR package, latest version.
Linux neko 4.17.2-1-ARCH #1 SMP PREEMPT Sat Jun 16 11:08:59 UTC 2018 x86_64 GNU/Linux