Option to keep open tabs when cleaning history

[ghost]

Hi, I mentioned this feature in #497 but it is not reflected in the title, so better to have it clearly here. The issue is simply to have an option to keep open tabs when cleaning history data. I personally like to keep a few tabs open for a while, but this should not come in the way of cleaning history and other data, so it would be good if deleting history could be done with the certainty of not losing open tabs. Thanks!