Show the branching structure in the log.

**Is your feature request related to a problem? Please describe.**
It can be useful seeing the branching/merging structure in the log view, in a similar way to `git log --oneline --decorate --graph`

**Describe the solution you'd like**
The graph view visible in the log window.

**Describe alternatives you've considered**
I haven't got any other alternatives other than not doing it. :-)