*8521* Introduce general section (for series and ojs section) constant and compatibility method
*8521* Introduce interface to retrieve section id (for series and ojs section)
*8521* Introduced metrics basic structure
*8521* Move common usage event plugin functionalities to lib
*8548* Introduce pkp lib path constant and use it
*8521* Introduced way to retrieve plugin template path in pkp library
*8521* Introduce acron plugin
*8521* Introduce general code for usage stats plugin
*8521* Introduce report plugin base class
*8521* Introduce interface to retrieve reports