inspect command: display "master" information instead of merge_base

[ThomasBuchinger]

As a user creating a PR targeted at master, I am expecting my changes to be applied on top of the current master.

However technically my feature branch may be behind master by several commits and git will "ignore" commits made after the feature branch branched from master. This is called the merge_base (commit) and is mostly invisible to the user unless there is a conflict.

The inspect command displays the actual merge_base commit, which may be confusing (at least I did not know about this concept). Instead it should display the current master information and an indication if the feature-branch is behind master and if conflicts exist