factor out a QueryCommand (super) class from SolrIndexSearcher.QueryCommand

part 0 (for trunk and branch_5x) - preparation:

• two minor changes in QueryComponent.java and SolrIndexSearcher.java to simplify the subsequent actual changes

part 1 (for trunk and branch_5x) - factor out a QueryCommand (super) class from SolrIndexSearcher.QueryCommand:

• for back-compat reasons SolrIndexSearcher.QueryCommand inherits from the factored out class
• for private variables and methods use QueryCommand instead of SolrIndexSearcher.QueryCommand
• public methods and constructors taking SolrIndexSearcher.QueryCommand args marked @Deprecated and equivalents with QueryCommand arg created

part 2 (for trunk only) - remove deprecated SolrIndexSearcher.QueryCommand class:

• affected/changed public or protected methods:
  • ResponseBuilder.getQueryCommand()
  • SolrIndexSearcher.search(QueryResult qr, QueryCommand cmd)
  • SolrIndexSearcher.sortDocSet(QueryResult qr, QueryCommand cmd)