Update metadata format to v2

Update the metadata format in a non backward compatible way to ease
the use of the service from 3rd party clients. The updated metadata
format is now more descriptive and HAL-compliant and can be used with
Spring HATEOAS to build a client.

Metadata v1 is still served to preserve backward compatibility with
Spring Boot 1.2.0.RC1.

Closes gh-49
Alias style to dependencies

Style is the only parameter that deviates from the default names in the
metadata. As 'dependencies' is the name used in the metadata, it can be
used as an alias of style. This simplifies the HAL-generated URLs

Fixes gh-50
Update to Spring Boot 1.1.9