added Julius as an always-on listener for 'computer'.

I added Julius speech recognition by altering listen.py and adding a folder called Julius containing the  grammar and vocab information. There are extra vocab words and grammar constructs than necessary to just listen for 'computer', but I have found that Julius without this extra information Julius tends to hear many false positives. Currently the extra vocab words and grammar were not added with any particular idea in mind, but in future work we can organize them more systematically.

I put all the code necessary for Julius to work in listen.py, because I was not sure how you wanted it organized. There is most likely a more efficient way of organizing the code that can be worked out. The code as it is works fine, but style and 'object-orientedness' could be improved on.

And as a last but obvious note, julius and julius-voxforge will need to be installed for the program to work. Let me know if you have any questions or comments!