Added font 'Chess Merida Unicode' and use that font in FEN mode

As a chess player I find the chess symbols from the default font very unusual. Some people might say the current symbols are not usable for learning. I would use the usual symbols like in chess books.
This request adds the 'chess merida unicode' font (see [1]) and small changes to the chess CSS file.
The font is according to [1] and [2] freeware.

Reference:
[1] http://mip.noekeon.org/HTMLTTChess/chess_merida_unicode.html
[2] http://www.enpassant.dk/chess/fonteng.htm

![screenshots](https://cloud.githubusercontent.com/assets/7302494/2719554/019c75b6-c563-11e3-87cf-24699fbe1206.png)