If there is only 1 commit is present in MR, apply patch buttun is enabled
allow to merge the MR in a single commit.

We show in small font size the same info that is shown on sign_in page:

    "GitLab Nexedi Edition", "About GitLab" and "About Nexedi"

This is good to have and hereby-introduced about-footer area will be
also used in the next patch for ICP too.

XXX placement of .about-footer to be near bottom is done not very
correctly.

= GitLab Community Edition + Nexedi patches

Include Merge description message in merge by default. User can disable description in merge message by clicking on `Don't include description in commit message`.

Drop the merge title which is "Merge branch SOURCE into TARGET" and only keep the MR title as commit message.

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