Util: Update private property names

* Prefix with underscore to identify as private
Util: `get_plugin_base()` retrieves parent's path
Util: Refactor `get_path_base()` and `get_plugin_base()`

* `get_path_base()` is core method
* `get_plugin_base()` uses `get_path_base()` to build plugin base value
Util: Refactor plugin info management

* Move all plugin info under single property (`$_plugin [array]`)
* Replace static method variable with instance properties where appropriate
Merge branch 'utils-anywhere' into develop
Admin: Use parent object to retrieve support link
Merge branch 'admin-anywhere' into develop