[4.4] Sync MoreBugUrl extension, add our custom patches

DO NOT COMMIT until Bugzilla has been upgraded to 4.4.

/template/en/custom/global/user-error.html.tmpl and
/Bugzilla/BugUrl.pm were removed as changes should not
go here, hence we now use the default upstream files.

/Bugzilla/BugUrl/Mingle.pm and
/Bugzilla/BugUrl/RequestTracker.pm and
/Bugzilla/BugUrl/SourceForgeAllura.pm were custom and
hence moved to /extension/MoreBugUrl/lib/.
Corresponding error messages were moved from
/template/en/custom/global/user-error.html.tmpl to
./extensions/MoreBugUrl/template/en/default/hook/global/user-error-bug_url_invalid_tracker.html.tmpl

/Bugzilla/BugUrl/GitHub.pm was synced with upstream.

./extensions/MoreBugUrl/Extension.pm requires code to
update the bug_see_also table, as we move several
files (Mingle, RequestTracker, SourceForgeAllura).

Also make sure that no "disabled" file is in the folder!

Bug: 56040
Change-Id: If91cb191c29f29e65a997f07e85fd4a4d8878a44