MINOR: pattern: add a new 'sample' type to store fetched data

MINOR: pattern: add a new 'sample' type to store fetched data

The pattern type is ambiguous because a pattern is only a type and a data
part, and is normally used to match against samples. Currently, patterns
cannot hold information related to the life of the data which was extracted.
We don't want to overload patterns either, so let's add a new "sample" type
which will progressively supersede the acl_test and maybe the pattern at most
places. The sample shares similar information with patterns and also has flags
describing the data volatility and protection.