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

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.

This reverts commit be048ae2.

- petclinic.css is now auto generated, therefore it is put in the
ignore list
- vendor folder is removed in favour of webjars
- remove several maven dependencies which are already managed by spring
boot
- unfortunately, lesscss maven plugin does NOT support importing from
classpath, as a result, bootstrap is unpacked during process-resources
phase, we need need to find a better resolution
- remove bower integration

- remove custom xml view, use springboot builtin xml view
- remove oxm maven dependency
- remove json-simple maven dependency (seems not relevant anymore)
- update vetsXml test using xpath

This reverts commit 4b1f7a7a.

#121