#336 Key generation: Improved consistency of entry editor

[fdar]

In the entry editor, the "Generate BibTeX key" icon is always visible on the left column (JabRef <= 2.2b).

For consistency, I think this icon should be located in the "Required fields" panel, to the right of the bibtexkey field.
Also, I think this would be a good practice to have the bibtexkey field displayed when the key is generated. It will encourage the user to pay attention to the new key.