Basic support for Solr 5.1 and above

[mkalkbrenner]

Beside a set of configuration files an update of solarium is required because of https://github.com/basdenooijer/solarium/commit/2157a3d2408f381c9dae7fca397d2fe2d250b090

[amateescu]

Discussed this with @mkalkbrenner and the Solr config files are the ones from https://www.drupal.org/sandbox/cpliakas/1600962.