file.open() checked everywhere except in loaders.
qWarning() message written to debug log, with error number and text.
We may want to exit OSCAR with a message in many situations, but that is not implemented yet.
Set number of debug logs to be kept for Release version to 4.
This uses the miniz library, which is self-contained in a single
.c/.h pair and has an MIT license.
Swapping out the zip library should be fairly straightforward
if ever necessary.
