Upgraded Jersey to 2.13.
#SB-228 Make it possible to manage repositories over REST
Committing WIP.

#SB-255: Create a service for the management of the strongbox.xml config file
Implemented.

#SB-263: Re-work the StorageBooter, so that it's no longer a testing mock implementation, but a proper booter instead
Implemented.

#SB-258: Make it possible to configure the strongbox.xml over REST
Committing WIP.

#SB-267: Create a RestClient for the non-artifact REST API
Committing WIP.

#SB-268: Replace XStream with JAXB
Implemented.

#SB-269: Re-work the ArtifactSearchService + SearchRestlet
Committing WIP.