A single CMake file with all build information

A new and improved CMake file.

Improvements:
- Replacement of all CMake files to a single file in order to ease understanding and maintenance (this avoids several files scattered in the repository).
- Environment variables (PATH, PYTHONPATH, NTA_ROOTDIR, etc) are set in own CMake file.
- Now it use the own Swig executable and dependencies located on External folder. Before this, I used 'find_packages' which could set an incompatible version for Nupic.
- Now it use the system python, i.e. the python package called from shell natively (similar to what Autotool version does). Before this, I used 'find_packages' which could set wrong python interpreter or libraries.

Build result: SUCCESS (including Swig modules!)

Tests results:
HtmTest: SUCCESS in all tests!!
TestEverything: 99.9107 %, only 1 (out of 2238) test failed: get spec of the dynamic library (i.e. libcpp_region).

I have worked hard to find out what is causing this, but without success.. :-( When I ignore TRY statement, it states that is not possible get a symbol from swig wrapped library:
dlopen(/Volumes/Data/Users/davidragazzi/nta/eng/lib/python2.7/site-packages/nupic/bindings/_math.so, 2): Symbol not found: __ZN14PySparseTensor3setERK13PyTensorIndexP7_object
  Referenced from: /Volumes/Data/Users/davidragazzi/nta/eng/lib/python2.7/site-packages/nupic/bindings/_math.so
  Expected in: flat namespace
 in /Volumes/Data/Users/davidragazzi/nta/eng/lib/python2.7/site-packages/nupic/bindings/_math.so

If some numenta expert could debug this, it would be great!