Updated gdcm to v2.4.4 and added options to generate Python bindings wit...

Updated gdcm to v2.4.4 and added options to generate Python bindings with SWIG. Supports :python and :python3.
The use of the `each_python` iterator there means the formula won't do anything without a python option, and will run make/make install twice if given both `with-python` and `with-python3`. If building with only one Python is supported (as seems to be implied by the cmake args), one should be given priority and `each_python` should not be used at all.
```
if build.with? "python"
  args << python2_cmake_args
elsif build.with? "python3"
  args << python3_cmake_args
end