[dataimport] Add SQL Store for faster import - works ONLY with Postgres for now, as it requires "copy from" command - closes #2410822 This store will use: - copy from for massive insertions. - execute from for update. The API of this store is similar to the other stores.

[test] swap order in assert of `test_users_and_groups_non_readable_by_guests` unittest2 order is (expected, got), not the opposite. This help test report readbility.

[test] fix server/querier/build_descr1 test. There is no self.transaction of TestCase. I assumed the test writer meant a session. This seems to make the test pass.