Added DTM wrapper, supports training on a corpus

What is included
-----------
* Initial implementation for the DTM wrapper. Made it look  like the Malletwrapper as much as possible (for consistency)
* Included a test_dtm script  to test out the model. I thought of putting this in the unittest, but was not sure. 
* Computes Influence Model by default
* Computes on any corpus that can be transoformed to BleiCorpus and has len (currently a part of my own research corpus is used).


To Run the test_script
-----------

* You just need to set the DTM_HOME variable or just supply the path to the binary.
* You can get the binaries either by compiling them from the  [original] or a [fork] ,which also has precompiled binaries for Linux and Windows.
* Supply another corpus if you wish .


What is missing
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* Inference on a holdout corpus.
* Tests
* Some comments and parameter explanations

P,S Still slightly new to the world of contributing with git. Please point out obvious mistakes.

 [original]:https://code.google.com/p/princeton-statistical-learning/downloads/detailname=dtm_release.tgz&can=2&q=
 [fork]:  https://github.com/magsilva/dtm