Many modifications in order to make a more efficient library for GNode creation

Many modifications in order to make a more efficient library for GNode creation
and graph management.

1) The xtream jar was uncompressed in order to use classes directly (Java
does not include jar within another jar)

2) The sigar library was deleted. Indeed, some problems with its use were difficult
to solve and another more important problem was found. With this library we obtain
system information, like processor frequency or amount of memory, but this not the
real information we need. Indeed, as we execute our program in a JVM, we should only
take into consideration what the JVM provide to us. So all information retrieved are
information about the JVM, which are: amount of available computing cores and memory
and the MegaFlops of a computing core.

3) In the grid class was added the computation of the heterogeneity degree of the
plate-form. This would be useful in designing a mapping algorithm which takes care
about this parameter.