This commit improves how custom application specify there version.
Previously, custom application were overriding variables like Slicer_VERSION_MAJOR
and this was causing build error because the #ifdef" using these variables
were not correct anymore.

With this change custom Slicer application can have their own metadata
(version number, description, ...) in addition of the Slicer ones.

To address this, this commit introduces application properties file and
its companion CMake function "SlicerReadApplicationProperties". This allows
to read the properties of a "Slicer application" before having to process
the corresponding sources. By using this new CMake function in the SlicerApplicationOptions
module included early in the custom application CMakeLists.txt, this
allows to display the application metadata without duplicating much code.

The vtkSlicerVersionConfigure.h was extented to include include these new
macros:
* Slicer_MAIN_PROJECT_VERSION
* Slicer_MAIN_PROJECT_VERSION_FULL
* Slicer_MAIN_PROJECT_BUILDDATE
* Slicer_MAIN_PROJECT_WC_URL
* Slicer_MAIN_PROJECT__WC_REVISION

when building Slicer, these macros are equivalent to Slicer_VERSION,
Slicer_VERSION_FULL, ...

Reviewed-by: Csaba Pinter <csaba.pinter@queensu.ca>
Reviewed-by: Andras Lasso <lasso@queensu.ca>

Tested-by: Pablo Hernandez <pablo.hernandez@kitware.com>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@27316 3bd1e089-480b-0410-8dfb-8563597acbee