branch upstream: Get initial steps

Get the initial steps, based on the commits in the local branch and on
the upstream.

branch upstream: integrate using the given steps

Given a set of steps, integrate the upstream changes to the local
branch.

branch upstream integration: merge commit

Add the ability to integrate changes by merge commit

WIP

wip: Merge by creating a full new commit

merge correctly

integration: Intial steps and display information

Author: estib-vega