ENH: Re-enable LoadPrivateTags option in GDCMImageIO

This feature was fixed by dc66c6c21c6058248b86022e4ac6dafc52233290,
but then removed by f00506be172c9d89314695788770e264f782a6d3. Reading
private tags should be fully supported by GDCM 2.x, so the option
should be made available.

The LoadPrivateTagsDefault option is not being restored, as it adds
unnecessary complexity and global state. Users wishing to change the
LoadPrivateTags or any other option can simply instantiate their own
GDCMImageIO object and pass it to ImageFileReader::SetImageIO().

Change-Id: Iedd1486d83f955e249511800fbdc13c2cf4af0a8
COMP: Fix all valid cppcheck warnings in "Module/Core" directory

The cppcheck is run inside the ITK/Module/Core directory and all the
valid cppcheck issues from four different categories are fixed. These
four categories are: performance, style, warning and error.

Some warnings are related to the intentionally created issues that are
provided in test files. Such warnings are an example of what I call
invalid warnings.

The titles of major fixed issues are listed below:

- prefix ++/-- operators are preferred for non-primitive types.
- emptiness of variables are checked in an efficient way.
e.g isntead of using
      if(Foo.size()==0)
    the
      if(Foo.empty())
    is used.
    or instead of using if(Foo.size()>0) the if(!Foo.empty()) is used.

- if possible, variables are passed by reference.
- initialization to assignment is preferred.
- if possible, the scope of variables are reduced.
- unused variables are removed.
- memory leaks are fixed.
- now a copy of the caught exception are thrown instead of rethrowing the
original exception.
- a default constructor is added to classes that did not have any constructor.
- some member variables were not initialized inside the constructors.

- Also, one special case is reported individually:
The if statement in line 264 of
"Modules/Core/Transform/test/itkCenteredEuler3DTransformTest.cxx" file
was false always. I replaced the && statement with ||
statement. This test is still passing after this change.

Finally I should mention that all the ITK tests are passed after the
above changes.

Change-Id: I4915f4a0c72aee910f05d06075c94efb82be7470
Merge branch 'master' into ModuleCore_cppcheck

Conflicts:
	Modules/Filtering/ImageFeature/test/itkHoughTransform2DCirclesImageTest.cxx
	Modules/Filtering/ImageFeature/test/itkHoughTransform2DLinesImageTest.cxx

Change-Id: Ic7d0129656b0db5f117e94b9fe0b8d0dc7a55e74
Merge topic 'ModuleCore_cppcheck'

dc36f28 Merge branch 'master' into ModuleCore_cppcheck
e56190c COMP: Fix all valid cppcheck warnings in "Module/Core" directory
Merge topic 'gdcm-private'

b2f5221 ENH: Re-enable LoadPrivateTags option in GDCMImageIO