The drag & drop behaviour of the text editor itself is kept as-is
(moving text blocks with the mouse etc., and also inserting file names
if dropped into the text area) because we don't want to re-implement all
of this ourselves.
However, we display a guidance text if a user drags files over the text
area telling them where to drop them to open.

Moreover, the license for the lines numbering has been clarified and is
now advertised in the About window

(old style cast, and "no out-of-line virtual method definitions")

The fonts are now setup in the constructor. An unnecessary script has
been deleted.

(it is licensed under BSD instead of GPL)