Make it possible to add markers to captured log files

[DanTup]

Sometimes log files are quite long and it's not always clear where the relevant parts are. It'd be nice if the logging notification had a button that let you add a marker to the log (eg. click it just before doing some relevant action, and it will log something distinctive at that point in the log file).

[DanTup]

Turns out we can't add additional buttons to progress notifications (and if we make it not a progress notifcation, it will hide itself after 10 seconds).