Sort commit graph by author date instead of commit date

[themilkman]

Problem description

E.g. when rebasing a big branch it'd be very useful to have the "original" commit and the rebased one near to each other.

Preferred solution

Add a possibility to switch the order of the commits/commit graph to the author date.

Alternatives

None that I could think of for this.

[srbs]

related: #1169 see also: #1100

[themilkman]

While I still struggle with the understanding and impact of the topological order which mixes in, this has been added in dev build 2081 and seems to work fine, thanks! :partying_face:

[themilkman]

When the topological order is equal (which is mostly the case on rebases) this works like a charm. Thanks again!