Build art_Framework_Art library and art/mu2e programs

Recurse build into art/Framework/Art directory. Update CMake commands
to configure sources, build, link and install targets:

- art_Framework_Art (lib)
- art (exe)
- art_ut (exe)
- mu2e (exe)
- mu2e_ut (exe)

Only difference between art/mu2e is default exception handling
policy. NAME_ut variants run the application inside Boost.Unit
test suite.

Add Boost.Unit library to list of needed libraries in top level
find_package call to support NAME_ut programs.

Add Root.Matrix library to list of needed Root libs in top
level find_package call to support art_Framework_Art.

Update README and Dependencies files to mark products as built.

NB: lar, gm2 and nova variants not built yet because these are
identical to basic art program. Implement later if absolutely
neccessary as softlinks.