non-blocking warning messages about fonts

[illwieckz]

On Linux:

$ ./updater2
QFontDatabase: Cannot find font directory /opt/Qt5.8-static-release/lib/fonts.
Note that Qt no longer ships fonts. Deploy some (from http://dejavu-fonts.org for example) or switch to fontconfig.

[DolceTriade]

It's ugly, but meh. I've tried to fix this, but this requires changing stuff in QT. My attempts to fix this have broken other things...

[slipher]

I also see this warning on Linux. But it seems to be spurious: we have Roboto-Regular.ttf in the resources directory and the typeface is displaying correctly.

[slipher]

On Mac there is the log message qt.qpa.fonts: Populating font family aliases took 650 ms. Replace uses of missing font family "Robot-Regular" with one that exists to avoid this cost. The text still looks correct, but maybe the one we ship is really not being used somehow.

[slipher]

I found that the font family name that we request needs to be Roboto rather than Roboto-Regular to fix the Mac warning. It turns out the Linux warning is unrelated and is still printed.