COMP: Remove unused TransformFileWriter::m_Precision ivar

Resolves issue 3183:

https://issues.itk.org/jira/browse/ITK-3183

Change-Id: Idefce0cb502d47c479d22969bc182d8ce38db569
Merge topic 'remove-dead-TransformFileWriter-m_Precision'

a05095d COMP: Remove unused TransformFileWriter::m_Precision ivar
ENH: transform reader/writer filters are templated on output precision type

Currently in the transform reader/writer classes of itk, the template
argument reflects the internal precision type of the input transform.
However, these classes should be able to get the input transform
precision type internally, and they should ask users just about the
expected precision type of the output transform.

Two different methods are used for Reader and Writer to enhance their
functionalities:

-Enhance TransformFileReader:
we convert the parameters precision types instantly when we read them
from transform buffer. Minimum changes are needed and just four
files (itkTransformBaseIO.hxx and itkHDF5/Txt/MatlabTransformIO.hxx)
are affected.

-Enhance TransformFileWriter:
Main changes are applied to "itkTransformFileWriter" filter files.
In this filter, "SetInput(TransformBaseTemplate<T> *transform)" function
has been changed to "SetInput(Object *transform)". While setting the
input transform, we cast its parameters value types to the requested
precision type one by one. Then, we continue the writing procedure
as before using the new converted input transform.

Change-Id: I7b008d5afed9218e60e52fda284c10133e16811a