Whats new page hidding

[rnr]

PR for #224
Added FF WHATS_NEW_IMAGE_OR_TITLE_TO_SKIP_PAGE - it can contain the image name or page title from the What's new JSON file. Pages with such image name or title will be skipped in the What's new function.
To test you can use this config https://github.com/edx/edx-mobile-config/tree/anton/whatsnew or add this to shared.yaml manually like:

UI_COMPONENTS:
    WHATS_NEW_IMAGE_OR_TITLE_TO_SKIP_PAGE: 'Learning Site Switching'

The process_config.py script has also been changed, it will now try to merge dictionaries from different files (e.g. iOS.yaml and shared.yaml) if both files have the same section with children in them

[saeedbashir]

@rnr As discussed over the huddle, this PR isn't needed as every version will be having it's own copy of whatsnew messages and images.

[rnr]

Looks like this should be resolved differently. Thanks to @saeedbashir for the clarification.