automake cleanup: implementing non-recursive make

- Enabling subdir objects
- Created a Makefile-env.am with basic automake init
- Created .am files per subdir, included from src/Makefile.am

Signed-off-by: Roald J. van Loon <roaldvanloon@gmail.com>
Merge pull request #577 from roaldvanloon/wip-automake

automake cleanup: implementing non-recursive make

Reviewed-by: Sage Weil <sage@inktank.com>