chg: gfanlib and gfanlib interface

updated source code of gfanlib and its interface to the newest version in master
(not properly embedded into Singular yet, to be fixed with future commit)
changed bigintmat in order to allow empty matrices
removed or commented out all traces of gfanlib and its interface in the folders
Singular/ and kernel/
(to be finally removed as soon as it is properly embedded into Singular)