fix output file differences between Lens and SpiNNaker

[lplana]

From pull request #29, output_mon_lens is no longer used. The generation of Lens-style output files is handled by function write_Lens_output_file ( ) in mlp_networks.py.

• Outputs reported are inconsistent in tick -1. lens reports 0 while SpiNNaker reports 0.5. lens itself is not consistent (output is 0 in rand10x40 and 0.5 in rogers - may have to do with output integrator in rand10x40).
• Lens reports the number of weight updates while SpiNNaker doesn't.
• Lens reports the actual number of ticks for every example while SpiNNaker reports the maximum.
• target values are not reported by Lens during the grace period while SpiNNaker does it in every tick.