First set of build system patches for Qt5 support.

These changes enable support for Qt5 in CTK libraries and CTK Qt plugins.
Set the CTK_USE_QT5 CMake variable to ON on specify the Qt5 installaltion
directory in QT5_INSTALL_PREFIX.
This commit enables Qt5 support for the CTK Core library, issue #277.

There is still a Qt5Widgets dependency, see issue #278. The tests
pass (on my Ubuntu 12.04 development machine) with both Qt4 and Qt5.
Add support for Qt5

Todo:
* Test with Qt4
* Make sure ctkMacroWrapPythonQt.cmake works correctly
Ensure edit line in ctkConsole is always visible

Even when the line is 2 line long.
Also, on Mac, typing Control (not Command) was resetting the cursor
to be at the end of the document.

Closes #295
Add open file dialog and print help message actions

Closes #315
API clean-up, documentation comments
ctkXnatScanResourceFile and ctkXnatReconstructionResourceFile unified to a single ctkXnatFile class
Unit test added for CTKXNATCore
XML Schema type property for ctkXnatObject
Schema type stored in ctkXnatObject
Remove unused FindCTK.cmake module

Since CTK targets are exported into a CTKConfig.cmake file, there is
no need for such module. It would simply add extra maintenance work
without real advantage.

See #397
Shared/weak pointers removed in favour of explicit memory handling
ctkXnatObject::addChild renamed to add
XNAT Core refactorings and basic support for creating objects
Existance test support
ctkXnatAPI class (former qXnatAPI from the qRestAPI project)
Parent can be passed to ctkXnatObject constructors
Unit test for XNAT object deletion
Proper pointer inizialization
XNAT save function save the properties