lib: Introduce WpSettings API

- Introduce wpsettings core object.
  - its a single ton object for a given metadata.
  - it provides the API to get/set settings and rules.
  - it is loaded by the main.c.
- add tests for the wpsettings object.
  - make changes in m-settings module and wpsettings object so that they work on the specified metadata object.
- add the rule parse logic.
  - wpsettngs object does this during its construction.
  - parses the rules in JSON config file into the wpinterest objects.
- add the _apply_rules() API and add lua bindings and corresponding tests.