Removed SR store implementation detail from wsrep-lib

The following was moved to application side implementation:

- Removed sr_store from streaming context.
- Removed sr_state from transaction.
- Removed get_binlog_cache() from client_service interface.

Other:
- Add SR applier reference to append_fragment_and_commit() to
  make it available for application.
- Add separate interface call to rollback SR transactions
  on disconnect. Rolling back SR transactions due to rollback
  fragment and rolling back SR transactions due to disconnect have
  different behaviors. Have separate calls for these different
  cases for clarity.
- Remove non-const transaction accessor, not needed anymore because
  SR state has been moved to application side.
- Remove unneeded set_fragments_from_table().

include/wsrep/streaming_context.hpp

@@ -47,7 +47,6 @@ namespace wsrep
             , fragment_size_()
             , unit_counter_()
             , log_position_()
-            , sr_store_(0)
         { }
 
         /**
@@ -190,17 +189,6 @@ namespace wsrep
             unit_counter_ = 0;
             log_position_ = 0;
         }
-
-        void set_sr_store(int store_type)
-        {
-            sr_store_ = store_type;
-        }
-
-        int get_sr_store() const
-        {
-            return (sr_store_);
-        }
-
     private:
 
         void check_fragment_seqno(wsrep::seqno seqno WSREP_UNUSED)
@@ -216,7 +204,6 @@ namespace wsrep
         size_t fragment_size_;
         size_t unit_counter_;
         size_t log_position_;
-        int sr_store_;
     };
 }