Allow changing the order of the columns in horizontal layout
In the History view, I'd like to have the commit graph in the center column instead of the commit details.
My main use-case for gitg is examining the history graph and ocasionally checking some commit details, and this disposition would put the focus on the graph itself.
This also feels like a more "natural" order of the columns (branches -> history -> commit). But I understand that there are many more use cases than mine, so I propose to have the order of the columns be configurable.