List widget should work without a key name

[ghost]

For example if I have such a _data file in Jekyll without an initial key, I can't add a new item with the list widget, cause it always has to have a name. Possible solution could be if the -name key is an empty string that should mean we don't want to have a name key, not undefined as is know.
This is the sample _data file I'd like to modify via the CMS:

[tech4him1]

This is somewhat related to #596, but it will probably require a separate implementation.

[tech4him1]

Duplicate of #531.