Import QRFS_* and QFT_* in query.py

Currently, the QRFT/QFT constants are used with the module (e.g.
constants.QRFS_NORMAL) in the query library. Given that there are 176
uses of these constants in a module that has roughly ~1200 lines in
total (including whitespace), it makes sense to import these directly to
improve readability.

This patch does this and (IMHO) it does indeed make the code more to the
point; the entire query library is about queries, so using these
constants directly doesn't cause any misunderstandings.

Note: the epydoc links are not changed, since we want the generated docs
to point to the right place.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>