Add title option for admin filter when providing a field name

[David Sanders]

The generated title for admin filters when the field is on a related model is often times confusing and not usable since it will be the name of the field without any reference to the fact that it's on a related model instead of the main model. When the field has the same name as a field on the main model it appears as a duplicate as far as the user can tell.

This patch expands the existing tuple pattern for a list_filter item to allow the second parameter to be a string which will be used as the title, instead of only allowing a class inheriting from FieldListFilter. This dove-tails nicely with the existing functionality as providing a subclass of FieldListFilter allows you to easily provide a title on the class itself, but the ability to provide just a string to use as a title removes the need to subclass the correct class choice for the field type (which is fragile) and streamlines the process for when you only want to change the title.

[pdecol]

​PR

[Mariusz Felisiak]

Proposed API is really confusing. There is already a clear and easy way to customize a title by subclassing a filter classes. I know that shortcuts are handy but isn't worth the additional complexity to the API. I discussed with Carlton and we agreed to close the ticket as wontfix.