Show critical error message and exit OSCAR if unable to write to data directory
Improve qWarning message in logger.cpp
Present warning dialog if logger cannot write to disk
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.
Also immediately emit debug messages to console even before the UI is
initialized.
And present a useful error if the OSCAR data folder can't be created.
This is transparent to the user and is recorded into a log directory within
the OSCAR_Data directory.
Also add log rotation so that these logs don't grow forever.
