Prevent creation of duplicate recipes

[kelson42]

By increasing the number of recipes and the number of people able to create and modify recipes, we increase as well the number of (potential) duplicate recipes. See for example openzim/zim-requests#560.

we should elaborate a solution to help users detect these duplicate early and warn them about the « danger ».

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be now be reviewed manually. Thank you for your contributions.