Pikabu Refactor

- More OO®
- Functions are now broken down into single responsibilities, and code's leaner, meaner and more testable
- Added QUnit tests
- API: openSidebar('right'), closeSidebars() and events for init, opened and closed
- Pikabu accepts settings (selectors for container, sidebars, overlay, nav; width of sidebars; events for init, open and close)
- Overlay is optionally dynamically generated (less HTML structure needed)
- Responsive behaviour (sidebars always visible on wider screens)
- Progressive enhancement (sidebars visible when JS is disabled)
- Added smooth scrolling to menu open toggler
- Misc improvements