LB-1503 Minor refactor to twitter-widget plugin

- Move waypoint require path to main.js, since it's shared by
scroll-paginationi plugin
- Use parentView method to access the parent view
LB-1389 Add scroll-pagination plugin
LB-1503 Use scroll-pagination plugin in default and stt themes
LB-1743 Fix bug: pending posts button not shown
Merge pull request #154 from patriciagarcia/LB-1389

LB-1503 Implement scroll pagination plugin