[FR] Default "New entry" type setting for custom sources

[thupsi]

A point of friction with custom sources is that it can get confusing when it comes to adding new entries: When the author clicks the "new entry" button she is likely presented with a long list of entry types that may be/seem unrelated to the current source.

I think it would help a lot if we could have a default new entry type for custom sources, so that the "new entry" button for the sources where this is configured would become a split button/button group, like on channels and structures:

This way the author could create new entries in a single click and without being confused.

Thanks for considering!