_**Closing this issue in favor of #150. Please participate there if any other comments.**_ ### Description This issue has to be done after #895 and is part of #411 . The idea is to squash commits together into one before merging a merge request. ### Specifications - Add an option in the Project settings to allow this functionality - Add a dropdown on the Merge Request screen with the option to squash commits - When selected, an input field and a textarea appear to let the user enter the squash commit message. ### Wireframes #### Option in the Settings panel of a project:  #### Flow in the Merge Request screen    ### Reference - Part of issue #411 (*Improve Merge Request accept flow with automatic rebase and option to squash*) - Related to #150 - Should be done after #895 (*Simplification of the merging process through the UI*) cc/ @JobV @DouweM