Remove libraries that user should not link directly from YARP_LIBRARIES
Rename YARPDependencies.cmake to YARPTarget.cmake

That's the name commonly used in CMake projects
Export libraries using the "YARP::" namespace

This is a common practice in CMake in order to separate targets
imported from other projects.

In order to link YARP libraries directly is now necessary to use (for
example)

  target_link_library(foo YARP::YARP_OS YARP::YARP_init)

WARNING: This commit breaks iCub in a couple of places and possibly
         other stuff (wherever YARP libraries are linked by name and
         not using YARP_LIBRARIES), and it is not backwards compatible.
link_directories should no longer be needed
Increment version tweak