ENH: Allow temporary directory to be accessible in MRML logics.

TemporaryPath is added to vtkMRMLApplicationLogic, so that the temporary directory can be directly accessible from MRML logics.

Also add associated tests

Fixes #2416

From: Yuzheng Zhou <yuzheng.zhou@kitware.com>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22229 3bd1e089-480b-0410-8dfb-8563597acbee