WIP: new add/edit forms, backend

[yild]

I'm currently working on add/edit attachment forms at backend side.

Interactive form, no reloads after changing parent type or url/file, but requires to change item handling from model file to tmp file.

Article/category standard select windows (same as used in Joomla Core). Different parent type can be added via plugin discovery and form XML change in code.

Still... its work in progress.

[reilldesign]

A drag & drop upload option would also be useful. Also for the editor xtd.