FS#13429: Add a freeform "player name" configuration setting

The idea is that a theme or whatever could use this to provide visual
differentiation (eg "George's iPod") between multiple
otherwise-identical players..

Defaults to an empty string.

Added to the manual but there is not a way to set this through the
menus yet.

Change-Id: I1cff6b19d621dd6207b4b82eed67741ce2da0ef1

manual/appendix/config_file_options.tex

@@ -384,6 +384,7 @@
       clear settings on hold
                 & off, on               & N/A\\
     }%
+    player name & freeform text, defaults to an empty string & N/A\\
     \bottomrule
   \end{longtable}
 \end{center}