add info about Acme resources
format, add JavaDoc
set jee version of wtp to 6 (Servlet 3)
rename JSONSerializer to JSON because it reads better for users
simplify Configuration and its test
rename JSONSerializer to JSON because it reads better for users (amend)
move db classes to core.model, drop DataAccessLayer abstraction, make
EntityManagerFactory also useable from tests
remove unused constructors from exceptions
drop empty test methods