matcaffe: Add command to get number of output channels

This number of outputs is what Caffe considers to be the number of "channels," which, for a fully connected layer, is the number of outputs.

New command is `caffe.caffe('get_num_output_channels')`.

Note that the new command is descriptive, but now screws up the aesthetics of the command list on matcaffe.cpp line 406. I could re-indent the list, shorten the command, or ignore it. The path of least resistance is to ignore it.