#620 Enriching the entry-view GUI

Why not enriching the entry view (which is very important for working with
literature) to a more comprehensive document information page? This might
include (beyond the current short-summary of the entry):
- the abstract
- the review
- icons for all attached files
- one-click buttons to copy the BibTeX Key
- one-click button to copy the \cite command
- one-click access to edit-fields for a certain part of the entry rather than navigating through the tabs of the entry-editor
- drag & drop support for attached files
- to/from the desktop
- to/from the mail client (Thunderbird, KMail, ...)