Add option to show unlabeled most recent common ancestor between all branches in Revision Graph.

What steps will reproduce the problem?
When looking at the revision graph, can often be hard to tell how closely related 2 branches are, if there are no labels in their ancestry.

For example, if your repository has 3 branches, master, branch_1 and branch_2. master has had additional commits added to it since branch_1 and branch_2 diverged from it. All 3 of these branches will currently show the a partial hash of the initial commit to the repository as their common parent, since no ancestor of any of these branches has a label.

What is the expected output? What do you see instead?

1. Add an option to the Revision Graph View menus, perhaps named Show unlabeled common ancestors.
2. When this option is enabled, for every 2 labels/branches on the Revision graph, a node will be shown on the graph for their most recent common ancestor. If this node has a label, the label will be shown. If the node has no label, a portion of the hash commit will be shown.

What version of TortoiseGit and Git are you using? On what operating system?

• TortoiseGit 2.8.0.0
• git version 2.18.0.windows.1