Changes algorithm in StimulusGroup

Makes changes to algorithm for binary patterns. Changes also the
behavior of the background rate.
Proposes a fix SparseConnection

This should fix the warning message that patterns are too large
in case where every parameters are correctly set and the warning
is not rightfully issued.
Changes SimpleMatrix and SparseConnection

Adds a serialization routine to SimpleMatrix and adds
multiple small bugfixes for loading matrices to SimpleMatrix
and SparseConnection.
Minor change to SparseConnection
Fixes a bug in SparseConnection

This fixes a bug that did only allow to load a single w matrix.
Fixing this allows to easily implement more complicated synaptic
dynamics.
Fixes bug in SparseConnection

This bug was introduced by the last commit and resulted in
empty weight matrices after a load_from_file operation. The
commit also changes when finalize() is called after a load
since it acts on w only and not on any particular matrices of
classes that inherit from SparseConnection.
Fixes bug in DuplexConnection

The bug caused memory reallocation in rare cases where
this was not necessary.
Updates debug Makefile