[dataimport] drop no more used parameter on massive store

[dataimport] methods that modify in-place shouldn't return value Also mark those methods private and drop some useless comments in passing. Related to #5414760

[dataimport] implement new store API on massive store and deprecate the old one. Related to #5414760

[dataimport] .finish method was missing from (NoHook)RQLObjectStore

[massive store] identity_relation should not be considered, is_relation seems missing The "identity_relation" table should not even exist.

[dataimport/test] use the right assert methods instead of assertTrue with a comparison

[dataimport] import range from six.moves

[dataimport/test] feed binary data to ucsvreader

[dataimport/test] fix broken comparison We want to compare two ints, not an int and a db row

[dataimport] dict.iteritems() → dict.items()

[dataimport] use next builtin instead of next method on iterators

[dataimport] import StringIO from io

[dataimport] backport massive store from dataio cube Some tweaks have been made to work with 3.21 foreign key constraints. Also test are not executed in our own pg cluster instead of polluting the system one. Closes #5414760

[web] set proper Cache-Control header for static files - set Cache-Control max-age to match Expires - use the max_age method (defaults to 1 week) instead of hardcoded 6 months

[web] use a redirect for /data/foo requests that don't use the instance md5 hash The actual file contents can be cached for a long time. If the request doesn't use the hash, that's wrong. Using a redirect lets keep the caching for the actual file contents while not breaking requests missing the hash.

[web] fix typo in doc string