Add option for date sort in an options menu

[jlpatter]

Right now it sorts first by date then topologically. It may be possible to sort topologically first then by date if either the branch order is dependent on the branches passed in to the revwalk or if we can build the tree one branch at a time and add them to a mainline.

[jlpatter]

Now it sorts first by topologically then by date. There should be an option in an options menu to switch between the two.