Closes gh-229

Encapsulation is better that way (and tere is a getter for all of them
anyway).

It's better maintained and it seems to provide more features
as well.

Vet, Owner, Visit. The Visit "aggregate" is a little artificial
but it demonstrates a useful point about not holding on to
references of "parent" (reference data) objects, i.e. the Visit has
an Integer petId, instead of a Pet field. In principle this app is
now almost ready to migrate to multiple services if anyone wanted
to do that.

I saw on twitter the reference of an article (in french):
http://javaetmoi.com/2016/08/migrer-vers-spring-boot/

That article concludes with something along the lines of  "Besides the
EhCache and Maven configuration, Petclinic does not hold a single line
of XML anymore".

Looking at the code, we can remove more XML if you want. This PR migrates
the cache infrastructure to EhCache 3 and JCache (JSR-107). This also
reduces the number of dependencies.

Merging AbstractClinicServiceTests and ClinicServiceSpringDataJpaTests then using the Spring Boot @DataJpaTest annotation

responsive menu fix - data-target attribute added

responsive menu fix - data-target attribute added

This reverts commit be048ae2.