Migrate to webjars for frontend resource management

- 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

Simplify content negotiation setup for vets 

- 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

Simplify jsp layout management

abstract the page layout into “layout.tag”

Support switching db init script at deployment

Fix #158 Improvements in VisitRepository.findByPetId implementation.

- In the Jdbc implementation: pets belonging to a visit were not added.
- In the Jpa implementation: query variable was wrong.
- Test case: AbstractClinicServiceTests.shouldFindVisitsByPetId()

General code quality fix-1

Fix of how to run Petclinic in readme

Fix #144 Redundant 'less than' symbol in exception.jsp

Update link navigation title to make it consistent

This reverts commit 4b1f7a7a.

Fixes #135 Fixed url for jquery-ui. 

owners search has been case insensitive

added missing .mvn folder needed for maven wrapper