remove the alias definition for symbolic color names

When using symbolic color names, we can drop the redefinition of the fill and draw colors.

This greatly reduces the file size. A fallback mechanism ensures the definitions are done as usual if either

 1. the maximal number of colors are exhausted or
 1. symbolic color names are switched off.
Is [`strlcpy`](http://www.gratisoft.us/todd/papers/strlcpy.html) available? If not, we should probably add an own copy of it. (I wish we used C++ already...)

See also https://randomascii.wordpress.com/2013/04/03/stop-using-strncpy-already/.