Attempt to automatically work out delimiter on import?

[caro401]

The errors you get when the delimiter is incorrectly set can be really confusing for users. We can have a pretty good idea of what the first (header) row of an import CSV should look like, because we specify in the plugin docs what this has to look like.

I think we might be able to help users by checking that parsing the first/header line with the provided delimiter gives a correct-looking result, and if not give the user a clear error message saying we think the delimiter setting might be wrong, and suggest what we think it should be and how to change that setting.

I don't think we should get rid of the existing configuration option or the default value ,, since this is also used when exporting. We should however make the docs about this setting more prominent

@flachware does this correctly summarise our earlier discussion?

[flachware]

Sounds good to me.