* Move some helpers from `acl/v2` package to `ape`. Also move errors;
* Introduce `Metadata`, `RequestInfo` types;
* Introduce `RequestInfoExtractor` interface and its implementation.
The extractor's purpose is to extract request info based on request
metadata. It also validates session token;
* Refactor ape service - each handler forms request info and pass
necessary fields to checker.
Signed-off-by: Airat Arifullin <a.arifullin@yadro.com>
