Display the namespace name before deleting it

### What does it do ?

Send the record data in `MODx.grid.Grid#remove` so we could use its attributes in lexicon.
Additionally, it now displays the name of a `modNamespace` in the confirmation window as well as disable the "remove" contextual menu for the "core" namespace.

### Why is it needed ?

When removing an object from a grid (ie. a namespace), we are prompted if we are sure about our action, but we have no idea if the selected record is indeed the one we are expecting to delete.

### Related issue(s)/PR(s)

* #2122