sql: introduce Tarantool's ephemeral tables

 - Added intermediate functions between SQL and Tarantool,
   tarantoolSqlite3Ephemeral* in order to create and use Tarantool's
   ephemeral tables. Also, for this reason added BTCF_TEphemeral flag to
   BtCursor instead of BTCF_TaCursor to call appropriate functions.
 - Added struct space* to SQL cursor, which allows to delete ephemeral
   tables.  (since ephemeral tables don't have space_id and it is
   impossible to find them by traditional space_id lookup). Moreover, it
   enables us to avoid using box API inasmuch as we can directly call
   space_execute_* functions having struct space*.
 - As the first stage of implemenation, ephemeral tables were
   successfully replaced for DELETE FROM ... WHERE statement. It utilized
   ephemeral space as intermediate holder where all tuples to be removed
   are placed before actual deletion.

Part of #2680