Add EventPrefix and EventObject to CMS Page/Block Collection

[osrecio]

Add EventPrefix to CMS Page Collection and CMS Block Collection

Description

Added EvenPrefix and EventObject for CMS Collections for instantiate observer for $this->_eventPrefix . '_load_after' and $this->_eventPrefix . '_load_before'

Fixed Issues (if relevant)

1. Cms module collections missing event prefix #9900

Manual testing scenarios

1. Add Observer for Event: cms_page_collection_load_after
2. Check Observer code is executed

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)