Add Find modules for Poco and TBB

Implement basic Find module for Poco using logic from top level
CMakeLists.txt. Only locate headers plus Foundation and Util libraries.
Use FindPackageHandleStandardArgs, only using location of headers and
Foundation library as requirements on Poco being found.

Import FindTBB module from Geant4 project (http://geant4.cern.ch).

Update build scripts for main project and examples to use new variables
defined by the Find modules.