Use FindPoco.cmake from ros/cmake_modules

This branch uses the FindPoco module from ros/cmake_modules

Fixes #21

Depends on ros/cmake_modules#26
I think this should be (according to the docs: http://www.cmake.org/cmake/help/v2.8.12/cmake.html#command:find_package):

    find_package(catkin REQUIRED COMPONENTS cmake_modules)