#107 Diagram in pgn-window

[Uwe]

In the PGN-Window "D" can be used as a NAG, which is intended to represent a diagram of the
position. So far the "D" has no effect. According to the output in the opening report, a diagram could
also insert in the PGN window. This should be enabled/disabled by options.
Note: Chessbase uses the sequence [#] in comments to display a diagram.
Both variants are not provided in the pgn-definition.

[Uwe]

possible implementation see https://github.com/benini/scid/pull/200