FIX: Generate ERP images

There are still problems when using the latest version of EEGLAB.
These are probably not related with meegpipe itself so for the
time being just use the older EEGLAB version that is available
at /data1/toolbox/eeglab2 (at somerengrid). Also, you will have
to use MATLAB R2011b because the latest MATLAB version (R2012a)
is not compatible with such older version of EEGLAB.