Improve crash log handling because of single-instance.
Never delete crash log file.

We also want to log to the crash log when segfaults happen during exit.
Remove unused faulthandler import.
Save lineparser even if there is no data.
Remove cookies when permissions->cookies-store was changed.

Fixes #116.
Add a simple wrapper around Qt's app.exec_().

This improves faulthandler tracebacks.
Split quickmarks correctly (from the right).

This was discovered in #189.