Improve SolrQuery class and add support for facet limit on per field basis in SolrJ

Currently the SolrQuery (org.apache.solr.client.solrj) class supports the setFacetLimit(int limit) and getFacetLimit() method.

Recently someone added a feature to specifiy the facet.limit on a per field basis. It would be great if this feature could be used from solrj.

with setFacetLimit(String field, int limit) and getFacetLimit(String field)
setFacetPrefix is already implemetned like this.