DATASOLR-144 - Add support for derived 'deleteBy...' queries.

Using keywords 'deleteBy...' or 'removeBy...' as well as '@Query(delete=false)' removes matching documents from solr.

Depending on the return type (List) the documents will be retrieved from the store prior to sending delete command. In case of numeric return type only the total number of removed documents is returned.

The method can be void as well.