STYLE: Removed legacy python importing

The preferred way to use itk with python is : import itk
The old way : from Insighttoolkit import *
I removed the old code which is no more needed.

See also : http://itk-users.7.n7.nabble.com/ITK-python-examples-td32400.html
STYLE: Pep8 cleanup for the python files

I cleaned up all the python files (they pass now the pep8 test)

Tool used to check pep8 :
- pip install pep8
- cd to Wrapping/Generators/Python
- pep8 . (to check all files)

Tool to automatically clean up the code :
- pip install autopep8
- autopep8 --in-place --aggressive --aggressive <filename>

Each file was manually checked after the autopep8 changes and manual adjustments were done when needed (the autopep8 tool helped a lot)

Additional changes :
- itkdata.py was renamed as itkData.py
- itktesting.py was renamed as itkTesting.py
- Some files had missing licence headers, I added them
- WrappingCoverage.py : removed python 2.3 compatibility stuff

There is still some deprecated stuff and unused variables to be removed, and more cleanup to be done
(the pyflakes and pylint tools are triggering a lot of warnings)
I did not run the tests (I think there will be some work to get them running).

So this is just a first step, it's not perfect but should allow to work through the code to keep it up to date with the newest python standards.

Change-Id: Ie244c57e00e2ad58050ca2a7f2e880aff6470bc2
BUG: No DiscreteHessianGaussianImageFunctionTest.

The itkDiscreteHessianGaussianImageFunctionTest is restored in this patch.

Checks have been added to bring the code coverage to 100%.

Error checking for images with zero spacing has been removed, since the
ImageBase class alreay performs those checks, making impossible for the error
to happen, and also making impossible to create a test case for the error case
previously considered in the original test.

Make use of the TestingMacros, so simplify the code.

Change-Id: I013cb7faf171880b1e4bb6b8cad1531e1af580ef
Merge topic 'itkDiscreteHessianGaussianImageFunction_CodeCoverage'

465355f5 BUG: No DiscreteHessianGaussianImageFunctionTest.
Merge topic 'remove-oldstyle-python-module'

399ee428 STYLE: Removed legacy python importing
Merge topic 'pep8-cleanup'

00fff70a STYLE: Pep8 cleanup for the python files