Expose data file's basename as attribute name

[ashmaroli]

This is to provide JekyllAdmin::DataFile instances parity with primitives from Jekyll.

Jekyll::Page, Jekyll::Document, Jekyll::StaticFile instances exposes their basename with extension via Liquid and therefore the API here as either :name or :basename

[mertkahyaoglu]

Cool. We can use this in the front-end now 👍

[ashmaroli]

We can use this in the front-end now

Yep. That's the idea.. 😃

[mertkahyaoglu]

Don't know why we didn't have this at the beginning 🤔

[ashmaroli]

Don't know why we didn't have this at the beginning

It was planned perhaps.. probably the reason why the private alias :filename was defined..
I've now removed that alias since it is just redundant..