Clean-up Acts headers

The Acts public header directories contained dozens of header files that should be private.

The header files for Gaudi/Athena components (algorithms, tools, services and converters) should ALWAYS reside in the src directory alongside their implementation (.cxx) files. Clients of tools and services should include a pure virtual interface header, of the public interface the component implements, which can be in the public include directory of the package, or in a dedicated interface library package.