Add featured image section to page settings.
Always activate featured images on page and post.
Move featured images methods to AbstractPost to make them available to Page.
Merge branch 'develop' into feature/Always_Activate_Featured_Images

Conflicts:
	WordPress/Classes/ViewRelated/Post/PostSettingsViewController.m
Refactor find featured media code
Merge pull request #2812 from wordpress-mobile/feature/Always_Activate_Featured_Images

Feature/always activate featured images