Commons events module refactor pages

Move events pages from commons_events module to commons_events_pages
module. The following patch was applied against commons 3.15 upstream:
- 0002-events-page-refactor-to-pages-module.patch

This patch allows to override the events page by groups modules.

Change-Id: I13ab0fd1c7644ecfc89768b70df3577578b4f00a