Test unordered logs

[hermankolden]

A production ULog in Aviant failed comparison with the original ULog
after write_ulog, which turned out to be because of messages arriving
at different times and thus the timestamps weren't completely in order.
This isn't really a problem, so we want the tests to pass, but in order
to do that we need the option of sorting the datasets.

[bkueng]

This is actually a problem in the writer as ulog files are required to have monotonically increasing timestamps.
It can happen though, and I'm ok with adding sorting but prefer to have it as separate method with appropriate comment.