Fixes DATASOLR-264 - Extended SolrTemplate to support multicore operations

[venilnoronha]

Firstly, I've created a new interface called MulticoreSolrOperations which is similar to SolrOperations, but, all methods in MulticoreSolrOperations accept a coreName parameter i.e. to specify a solr core over which the operation should be performed. SolrTemplate now implements MulticoreSolrOperations and it heavily depends on the SolrClientFactory instance. It means that these operations would be executed on the specified Solr core only if SolrTemplate was wired with MulticoreSolrClientFactory and not HttpSolrClientFactory (as it returns the same SolrClient instance for any coreName given to its getSolrClient method).

The fix for the issue didn't have anything to do with what I've described above i.e. it was just about extracting the coreName from SolrDocument annotated over SolrsearchRequestProductData while executing SolrTemplate#queryForFacetPage(query, SolrsearchRequestProductData.class) and performing the operation over that core. To be consistent, I modified all implemented methods of SolrOperations inside SolrTemplate to use the newly created SolrClientUtils#resolveSolrCoreName(Class<?> type, String defaultCoreName) method wherever a Class was present in the method parameters. This however didn't seem to be a complete solution as not all methods were, in a sense, "multicore" supportive i.e. methods like commit couldn't operate on a core other than the default one. This was the reason for creatingMulticoreSolrOperations.

Please review and pull if the solution looks fine. My CLA number is 149720151120072904.

Thanks, Venil Noronha