Adds functionality to SpikingGroup

This adds a method that can initialize a StateVector
with random Gaussian noise.
Fixes a typo in comment
Fixes problem in SparseConnection

In particular it adds a finalize to load_from_complete_file in
SparseConnection and adds an additional check for size in the
DuplexConnection finalize function in which a reverse matrix can
be resized before being computed.
Fixes bug in new scale function
Adds logging output
Adds a new setter to StimulusGroup

The setter set_stimulus_mode allows to explicitly set and
change the stimulus presentation order during a simulation.
Adds new mode to StimulusGroup

The new mode now allows to read the stimulus order
from a stimfile instead of generating it randomly.

To use the mode it needs to be called in the constructor
otherwise it will cause problems with the file init.
Minor improvement in SparseConnection
Removes debugging output in StimulusGroup.cpp